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You can find a wide range of solved case studies on myCBSEguide, covering various topics and concepts. Class 9 Science case studies are designed to help you understand the application of various concepts in real-life situations.

The rationale behind Science

Science is crucial for Class 9 students’ cognitive, emotional, and psychomotor development. It encourages curiosity, inventiveness, objectivity, and aesthetic sense.

In the upper primary stage, students should be given a variety of opportunities to engage with scientific processes such as observing, recording observations, drawing, tabulating, plotting graphs, and so on, whereas in the secondary stage, abstraction and quantitative reasoning should take a more prominent role in science teaching and learning. As a result, the concept of atoms and molecules as matter’s building units, as well as Newton’s law of gravitation, emerges.

Science is important because it allows Class 9 Science students to understand the world around us. It helps to find out how things work and to find solutions to problems at the Class 9 Science level. Science is also a source of enjoyment for many people. It can be a hobby, a career, or a source of intellectual stimulation.

Case study questions in Class 9 Science

The inclusion of case study questions in Class 9 science CBSE is a great way to engage students in critical thinking and problem-solving. By working through real-world scenarios, Class 9 Science students will be better prepared to tackle challenges they may face in their future studies and careers. Class 9 Science Case study questions also promote higher-order thinking skills, such as analysis and synthesis. In addition, case study questions can help to foster creativity and innovation in students. As per the recent pattern of the Class 9 Science examination, a few questions based on case studies/passages will be included in the CBSE Class 9 Science Paper. There will be a paragraph presented, followed by questions based on it.

Examples of Class 9 science class case study questions

Class 9 science case study questions have been prepared by myCBSEguide’s qualified teachers. Class 9 case study questions are meant to evaluate students’ knowledge and comprehension of the material. They are not intended to be difficult, but they will require you to think critically about the material. We hope you find Class 9 science case study questions beneficial and that they assist you in your exam preparation.

The following are a few examples of Class 9 science case study questions.

Class 9 science case study question 1

due to its high compressibility
large volumes of a gas can be compressed into a small cylinder
transported easily
all of these
shape, volume
volume, shape
shape, size
size, shape
the presence of dissolved carbon dioxide in water
the presence of dissolved oxygen in the water
the presence of dissolved Nitrogen in the water
liquid particles move freely
liquid have greater space between each other
both (a) and (b)
none of these
Only gases behave like fluids
Gases and solids behave like fluids
Gases and liquids behave like fluids
Only liquids are fluids

Answer Key:

(d) all of these
(a) shape, volume
(b) the presence of dissolved oxygen in the water
(c) both (a) and (b)
(c) Gases and liquids behave like fluids

Class 9 science case study question 2

12/32 times
18 g of O 2
18 g of CO 2
18 g of CH 4
1 g of CO 2
1 g of CH 4 CH 4
2 moles of H2O
20 moles of water
6.022 × 1023 molecules of water
1.2044 × 1025 molecules of water
(I) and (IV)
(II) and (III)
(II) and (IV)
Sulphate molecule
Ozone molecule
Phosphorus molecule
Methane molecule
(c) 8/3 times
(d) 18g of CH 4
(c) 1g of H 2
(d) (II) and (IV)
(c) phosphorus molecule

Class 9 science case study question 3

collenchyma
chlorenchyma
It performs photosynthesis
It helps the aquatic plant to float
It provides mechanical support
Sclerenchyma
Collenchyma
Epithelial tissue
Parenchyma tissues have intercellular spaces.
Collenchymatous tissues are irregularly thickened at corners.
Apical and intercalary meristems are permanent tissues.
Meristematic tissues, in its early stage, lack vacuoles, muscles
(I) and (II)
(III) and (I)
Transpiration
Provides mechanical support
Provides strength to the plant parts
None of these
(a) Collenchyma
(b) help aquatic plant to float
(b) Sclerenchyma
(d) Only (III)
(c) provide strength to plant parts

Cracking Class 9 Science Case Study Questions

There is no one definitive answer to Class 9 Science case study questions. Every case study is unique and will necessitate a unique strategy. There are, nevertheless, certain general guidelines to follow while answering case study questions.

To begin, double-check that you understand the Class 9 science case study questions. Make sure you understand what is being asked by reading it carefully. If you’re unclear, seek clarification from your teacher or tutor.
It’s critical to read the Class 9 Science case study material thoroughly once you’ve grasped the question. This will provide you with a thorough understanding of the problem as well as the various potential solutions.
Brainstorming potential solutions with classmates or other students might also be beneficial. This might provide you with multiple viewpoints on the situation and assist you in determining the best solution.
Finally, make sure your answer is presented simply and concisely. Make sure you clarify your rationale and back up your claim with evidence.

A look at the Class 9 Science Syllabus

The CBSE class 9 science syllabus provides a strong foundation for students who want to pursue a career in science. The topics are chosen in such a way that they build on the concepts learned in the previous classes and provide a strong foundation for further studies in science. The table below lists the topics covered in the Class 9 Science syllabus of the Central Board of Secondary Education (CBSE). As can be seen, the Class 9 science syllabus is divided into three sections: Physics, Chemistry and Biology. Each section contains a number of topics that Class 9 science students must study during the course.

CBSE Class 9 Science (Code No. 086)

Theme: Materials Unit I: Matter-Nature and Behaviour Definition of matter; solid, liquid and gas; characteristics – shape, volume, density; change of state-melting (absorption of heat), freezing, evaporation (cooling by evaporation), condensation, sublimation. Nature of matter: Elements, compounds and mixtures. Heterogeneous and homogenous mixtures, colloids and suspensions. Particle nature and their basic units: Atoms and molecules, Law of constant proportions, Atomic and molecular masses. Mole concept: Relationship of mole to mass of the particles and numbers. Structure of atoms: Electrons, protons and neutrons, valency, the chemical formula of common compounds. Isotopes and Isobars.

Theme: The World of the Living Unit II: Organization in the Living World Cell – Basic Unit of life: Cell as a basic unit of life; prokaryotic and eukaryotic cells, multicellular organisms; cell membrane and cell wall, cell organelles and cell inclusions; chloroplast, mitochondria, vacuoles, endoplasmic reticulum, Golgi apparatus; nucleus, chromosomes – basic structure, number. Tissues, Organs, Organ System, Organism: Structure and functions of animal and plant tissues (only four types of tissues in animals; Meristematic and Permanent tissues in plants).

Theme: Moving Things, People and Ideas Unit III: Motion, Force and Work Motion: Distance and displacement, velocity; uniform and non-uniform motion along a straight line; acceleration, distance-time and velocity-time graphs for uniform motion and uniformly accelerated motion, derivation of equations of motion by graphical method; elementary idea of uniform circular motion. Force and Newton’s laws: Force and Motion, Newton’s Laws of Motion, Action and Reaction forces, Inertia of a body, Inertia and mass, Momentum, Force and Acceleration. Elementary idea of conservation of Momentum. Gravitation: Gravitation; Universal Law of Gravitation, Force of Gravitation of the earth (gravity), Acceleration due to Gravity; Mass and Weight; Free fall. Floatation: Thrust and Pressure. Archimedes’ Principle; Buoyancy. Work, energy and power: Work done by a Force, Energy, power; Kinetic and Potential energy; Law of conservation of energy. Sound: Nature of sound and its propagation in various media, speed of sound, range of hearing in humans; ultrasound; reflection of sound; echo.

Theme: Food Unit IV: Food Production Plant and animal breeding and selection for quality improvement and management; Use of fertilizers and manures; Protection from pests and diseases; Organic farming.

PRESCRIBED BOOKS:

Science-Textbook for class IX-NCERT Publication
Assessment of Practical Skills in Science-Class IX – CBSE Publication
Laboratory Manual-Science-Class IX, NCERT Publication
Exemplar Problems Class IX – NCERT Publication

myCBSEguide: A true helper

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myCBSEguide offers high-quality study materials that cover all of the topics in the Class 9 Science curriculum.
myCBSEguide provides practice questions and mock examinations to assist students in the best possible preparation for their exams.
On our myCBSEguide app, you’ll find a variety of solved Class 9 Science case study questions covering a variety of topics and concepts. These case studies are intended to help you understand how certain principles are applied in real-world settings
myCBSEguide is that the study material and practice problems are developed by a team of specialists who are always accessible to assist students with any questions they may have. As a result, students may be confident that they will receive the finest possible assistance and support when studying for their exams.

So, if you’re seeking the most effective strategy to study for your Class 9 Science examinations, myCBSEguide is the place to go!

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Case Study Questions of Chapter 4 Structure of Atom PDF Download

Case study Questions on Class 9 Science Chapter 4 are very important to solve for your exam. Class 9 Science Chapter 4 Case Study Questions have been prepared for the latest exam pattern. You can check your knowledge by solving case study-based questions for Class 9 Science Chapter 4 Structure of Atom

In CBSE Class 9 Science Paper, Students will have to answer some questions based on Assertion and Reason. There will be a few questions based on case studies and passage-based as well. In that, a paragraph will be given, and then the MCQ questions based on it will be asked.

Structure of Atom Case Study Questions With answers

Here, we have provided case-based/passage-based questions for Class 9 Science Chapter 4 Structure of Atom

Case Study/Passage Based Questions

The maximum number of electrons that are permitted to be assigned to an energy shellb of an atom is called the electron capacity of that shell. The distribution of electrons in different orbits or shell is governed by a scheme known as Bohr-Bury scheme. According to this scheme : (i) The maximum number of electrons that can be present in any shell is given by the formula 2n2 where n is the number of energy levels. (ii) The maximum number of electrons that can be accommodated in the outermost shell is 8. Electrons are filled in the shells in a stepwise manner in increasing the order of energy of the energy shell.

What is the maximum electrons capacity of the N shell? (a) 24 (b) 8 (c) 18 (d) 32

Answer: (d) 32

Identify the element with the configuration K-2, L-8, M-3. (a) Aluminium (b) Magnesium (c) Sodium (d) Beryllium

Answer: (a) Aluminium

Which of the following configuration represent sodium? (a) 2, 8, 4 (b) 2, 8, 5 (c) 2, 3 (d) 2, 8, 1

Answer: (d) 2, 8, 1

The given diagrams show the atomic structures of elements X and Y.

Element X and Y could be _ and _ respectively. (a) Be and B (b) C and O (c) F and N (d) C and N

Answer: (d) C and N

Valency of elements X and Y are respectively, (a) 4 and 3 (b) 2 and 5 (c) 1 and 4 (d) 3 and 4

Answer: (a) 4 and 3

Elements X and Y are (a) isotopes (b) isoelectronic (c) isobars (d) isomers.

Answer: (c) isobars

The mass of an atom is due to the masses of protons and neutrons in the nucleus. The relative masses of protons and neutrons are almost equal to one. Therefore, the atomic mass of an element should be nearly a whole number. But in many cases the atomic masses are fractional. The main reason for these fractional atomic masses is that these elements occur in nature as a mixture of several isotopes. The atomic mass of an element is the average of the atomic masses of these isotopes in the ratio of their proportion of occurrence.

Chlorine occurs in nature in the form of two isotopes with atomic masses 35 u and 37 u in the ratio of 3 : 1 respectively. The atomic mass of chlorine is (a) 35.5 u (b) 34.5 u (c) 35 u (d) 36 u

Answer: (a) 35.5 u

An element occurs in two isotopic forms with atomic masses 10 and 11. What is the percentage abundance of two isotopes in the sample having an atomic mass of 10.80? (a) 20, 80 (b) 50, 50 (c) 25, 70 (d) 60, 40

Answer: (a) 20, 80

The fractional atomic masses of elements are due to the existence of (a) isotopes having different masses (b) diagonal relationship (c) equal number of electrons and protons (d) none of these.

Answer: (a) isotopes having different masses

Hope the information shed above regarding Case Study and Passage Based Questions for Class 9 Science Chapter 4 Structure of Atom with Answers Pdf free download has been useful to an extent. If you have any other queries of CBSE Class 9 Science Structure of Atom Case Study and Passage Based Questions with Answers, feel free to comment below so that we can revert back to us at the earliest possible

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NCERT Solutions for Class 9 Science Chapter 4 - Structure Of The Atom
NCERT Solutions

Download NCERT Solutions for Class 9 Science Chapter 4 - free PDF

Class 9 Science Chapter 4 describes the structure of the atom. In this chapter, students will discover novel ideas and hypotheses that have been developed and validated by several scientists. Applying the newly taught ideas would be much simpler if you use the Vedantu-prepared NCERT Solutions for Class 9 Science Chapter 4.

For CBSE Class 9 Chapter 4, Vedantu offers NCERT answers that have been created by subject-matter experts. To succeed in your studies, get the NCERT answer that our professionals have offered. The answers to the NCERT practice questions are provided in a step-by-step manner using the simple-to-understand format of pdf. The solutions to every question in the Class 9 curriculum are included in the NCERT answers pdf. Begin your study process under the direction of the Vedantu experts and ace your tests.

List of Topics Covered Under NCERT Solutions for Class 9 Science Chapter 4

A glance about the topic .

Atoms contains positively charged Protons, negatively charged electrons and the neutral charged Neutrons

Thomson model, Rutherford model and Bhor’s model attempted various experiments for finding the structure of atoms and position of electrons, protons and neutrons.

The total number of protons present in the atom is known as the atomic number.

The total number of protons and neutrons in the atom is known as the mass number.

An atom with the same atomic number and different mass number is known as Isotopes.

An atom with a different atomic number and the same mass number is known as Isobars.

Access NCERT Solutions for Science Class 9 Chapter 4 – Structure of the Atom

Intext Questions:

1. What are canal rays?

Ans: Canal rays are beams of positively charged ions. It was discovered in 1886 by Goldstein. Canal rays are also known as anode rays.

2. If an atom contains one electron and one proton, will it carry any charge or not?

Ans: An atom carrying one electron and one proton will carry no charge as the negatively charged particle will combine with the positively charged particles and the overall magnitude of the atom will be zero.

3. On the basis of Thomson’s model of an atom, explain how the atom is neutral as a whole.

Ans: According to Thomson’s model of the atom:

1. An atom consists of both negatively and positively charged particles.

2. The negatively charged particles are embedded in the positively charged sphere.

3. These negative and positive charges are equal in magnitude.

4. They counterbalance each other’s effect and make an atom neutral.

4. On the basis of Rutherford’s model of an atom, which subatomic particle is present in the nucleus of an atom?

Ans: According to Rutherford’s model of an atom, protons are present in the nucleus of an atom.

5. Draw a sketch of Bohr’s model of an atom with three shells.

6. Name the three subatomic particles of an atom.

Ans: Three subatomic particles of an atom are as follows:

ii. Electron

iii. Neutron.

7. Helium atom has an atomic mass of 4 u and two protons in its nucleus. How many neutrons does it have?

Ans: Number of protons in Helium Atom = \[2\]

Atomic Mass = Number of Protons + Number of Neutrons

$4=2+\text{ Number of Neutrons}$

$ \text{Number of Neutrons = 4 - 2 = 2}$

8. Write the distribution of electrons in carbon and sodium atoms?

Ans: Atomic number of carbon = \[6\] = Number of protons = Number of electrons

The distribution of electrons in carbon atom is given by:

First orbit or K-shell = $2$ electrons

Second orbit or L-shell = $4$ electrons

or, we can write the distribution of electrons in a carbon atom as $2,4$

Atomic number of sodium = $11$= Number of protons = Number of electrons

The distribution of electrons in sodium atom is given by:

Second orbit or L-shell = $8$ electrons

Third orbit or M-shell = $1$ electron

Or, we can write the distribution of electrons in a sodium atom as \[2,\text{ }8,1\].

9. If K and L shells of an atom are full, then what would be the total number of electrons in the atom?

Ans: Maximum number of electron in K-shell = $2$

Maximum number of electron in L-shell = $8$

If K and L-shells of an atom are full,

then the total number of electrons in the atom would be \[\left( 2\text{ }+\text{ }8 \right)\text{ }=\text{ }10\]electrons.

10. How will you find the valency of chlorine, sulphur and magnesium?

If the number of electrons in the outermost shell is less than $4$ then,

Valency of an atom = number of electrons in the outermost shell of the atom.

In the case of magnesium,

Thus, the valency of magnesium = $2$

If the number of electrons in the outermost shell is less than 4 then,

Valency of an atom = 8 – Number of electrons in the outermost shell.

In case of sulphur,

The valency of sulphur = 8 − 6 = 2

In case of chlorine,

The valency of chlorine = 8 −7 = 1

11. If the number of electrons in an atom is 8 and the number of protons are also 8, then

(i) What is the atomic number of the atom and (ii) What is the charge on the atom?

1. The atomic number = number of protons.

Hence, the atomic number of the atom is $8$.

2. Since the number of both electrons and protons is equal, therefore, the charge on the atom is $0$ i.e., it is a neutral atom.

12. With the help of Table 4.1, find out the mass number of oxygen and sulphur atom.

Ans: Mass number = Number of protons + Number of neutrons

Mass number of $\mathrm{O}_{2}=8+8=16$

Mass number of $\mathrm{S}=16+16=32$

13. For the symbols H, D and T tabulate three sub-atomic particles found in each of them.

14. Write the electronic configuration of any one pair of isotopes and isobars.

Two isotopes of carbon are :

${ }_{6}^{12} \mathrm{C}$

${ }_{6}^{14} \mathrm{C}$

The electronic configuration of ${ }_{6}^{12} \mathrm{C}$ is $2,4$

The electronic configuration of ${ }_{6}^{14} \mathrm{C}$ is $2,4$

Two isobars of carbon are :

${ }_{20}^{40} \mathrm{Ca}$

${ }_{18}^{40} \mathrm{Ar}$

The electronic configuration of ${ }_{20}^{40} \mathrm{Ca}$ is \[\text{2, 8, 8, 2}\text{.}\]

The electronic configuration of ${ }_{18}^{40} \mathrm{Ar}$ is \[\text{2, 8, 8}\text{.}\]

Exercise Questions:

1. Compare the properties of electrons, protons and neutrons.

Ans: The difference between electron, proton and neutrons are as follows:

2. What are the limitations of J.J. Thomson’s model of the atom?

Ans: Limitations of J.J. Thomson’s model of the atom.

It fails to explain the stability of an atom.

It doesn’t talk about the nucleus of an atom.

It failed to explain the reason for positive and negative charges binding together.

It also doesn’t explain Rutherford’s model.

3. What are the limitations of Rutherford’s model of the atom?

Ans: Rutherford’s model of the atom fails to explain the stability of an atom. He argued that electrons move in a circular path called the orbit. The Revolution of electrons in the orbit will radiate energy which will make the atom unstable and electrons will fall inside the nucleus. But in reality this is not the case and Rutherford’s model fails to explain the reason for the same.

4. Describe Bohr’s model of the atom.

A Sketch of Bohr’s model of an atom with three shells.

5. Compare all the proposed models of an atom given in this chapter.

Ans : Comparison of all models of an atom are given below:

6. Summarize the rules for the writing of the distribution of electrons in various shells for the first eighteen elements.

Ans: For the first eighteen elements, the rules for writing the distribution of electrons in various shells are as follows:

1. The maximum number of electrons that a shell can accommodate is determined by the formula ‘$\text{2}{{\text{n}}^{\text{2}}}$’, where ‘$\text{n}$’ is the orbit number \[\left( n\text{ }=\text{ }1,\text{ }2,\text{ }3\ldots \right).\] The maximum number of electrons present in an orbit of $\text{n = 1}$ is given by $\text{2}{{\text{n}}^{\text{2}}}=2{{(1)}^{2}}=2$

Again for second orbit, it is $\text{2}{{\text{n}}^{\text{2}}}=2{{(2)}^{2}}=2\times 4=8$

For third orbit, it is $\text{2}{{\text{n}}^{\text{2}}}=2{{(3)}^{2}}=2\times 9=18$

2. The outermost orbit can hold a maximum of eight electrons.

3. Shells are filled with electrons in a stepwise manner, with the inner shells being filled first, followed by the outer shells.

7. Define valency by taking examples of silicon and oxygen.

Ans: Valency of an element is defined as the number of electrons in its outermost shell.

In the case of silicon,

Outermost shell electron = $4$

If the number of electrons in the outermost shell of the atom of an element is less than or equal to $4$,

Valency of an atom = number of electrons in the outermost shell

Thus, the valency of silicon = $4$.

In the case of oxygen,

Outermost shell electron = \[6\]

If the number of electrons in the outermost shell of the atom of an element is greater than $4$,

Then, the valency of an atom = $8$ – Number of electrons in the outermost shell.

Thus, the valency of oxygen is \[\left( 8\text{ }-\text{ }6 \right)\text{ }=\text{ }2\].

8. Explain with examples.

i. Atomic number

ii. Mass number,

iii. Isotopes

iv. Isobars.

Give any two uses of isotopes.

i. Atomic Number: Total number of protons present in the atom of an element is called the atomic number of that element.

Example: Oxygen has $8$ protons. Thus, the atomic number of Oxygen is $8$.

ii. Mass Number: The sum of the number of protons and neutrons present in the atom of an element is called the mass number.

Example: Oxygen has $8$ protons and $8$ neutrons.

Therefore the mass number of oxygen is $8+8=16$

iii. Isotopes: Isotopes are atoms of the same element having the same atomic number, but different mass numbers.

Example : Three isotopes of Hydrogen are:

1) Protium $\left({ }^{1} \mathrm{H}\right)$

2) Deuterium $\left({ }_{1}^{2} \mathrm{H}\right)$

3) Tritium $\left({ }_{1}^{3} \mathrm{H}\right)$

(iv). Isobars: Isobars are atoms with the same mass number but different atomic numbers, i.e., isobars are atoms with the same mass number from different elements.

Example: ${ }_{20}^{40} \mathrm{Ca} \text { and }{ }_{18}^{40} \mathrm{Ar} \text { are two isobars. }$

9. Na+ has completely filled K and L shells. Explain.

Ans: Atomic number of Na = 11 = Total number of electrons

The electronic configuration of Na = 2, 8, 1.

The electronic configuration of Na+ ion = 2 (K-shell), 8 (L-shell)

Thereby Na+ ion has completely filling K and L shells.

10. If bromine atom is available in the form of, say, two isotopes ${ }_{35}^{79} \mathrm{Br}(49.7 \%) \text { and }{ }_{35}^{81} \mathrm{Br}(50.3 \%)$ calculate the average atomic mass of bromine atom.

Ans : Average atomic mass of Bromine atom

= \[\dfrac{\left[ 79\times 49.7~+~81\times 50.3 \right]}{100}\]

$ =\dfrac{3926.3+4074.3}{100}$

$ =\dfrac{8000.6}{100}$

=80.006

$\approx 80\text{u}$

11. The average atomic mass of a sample of an element X is \[16.2\text{ u}\]. What are the percentages of isotopes ${ }_{8}^{16} \mathrm{X}$ and ${ }_{8}^{18} \mathrm{X}$ in the sample?

Ans: Average atomic mass of an element X = \[16.2\text{ u}\]

Let percentage of isotope ${ }_{8}^{18} \mathrm{X}$ is $y%$

Thus, the percentage of isotope ${ }_{8}^{18} \mathrm{X}$ is $(100-y)%$

Average atomic mass of element X= [Atomic mass of ${ }_{8}^{18} \mathrm{X}$ $\times $ percentage + Atomic mass of ${ }_{8}^{16} \mathrm{X}$ $\times $ percentage ]

$16.2=[18 \times y \%+16 \times(100-y) \%]$

$16.2=\left[18 \times \dfrac{y}{100}+16 \times \dfrac{(100-y)}{100}\right]$

$16.2 \times 100=[18 y+1600-16 y]$

$1620=2 y+1600$

$1620-1600=2 y$

$y=\dfrac{20}{2}$

Thus, percentage of ${ }_{8}^{16} \mathrm{X}$ is $10%$

Percentage of ${ }_{8}^{16} \mathrm{X}$ is $(100-10)=90%$

12. If Z = 3, what would be the valency of the element? Also, name the element.

Ans: Atomic number \[=\text{ }Z\text{ }=\text{ }3.\]

Its electronic configuration is 2, 1.

Hence, the valency of the element is 1

(Since the outermost shell has only one electron).

Therefore, the element with Z = 3 is lithium (Li).

13. Composition of the nuclei of two atomic species X and Y are given as under X Y

Give the mass numbers of X and Y. What is the relation between the two species?

Mass number of \[X\text{ }=\text{ }6\text{ }+\text{ }6\text{ }=\text{ }12\]

Mass number = Number of protons + Number of neutrons

Mass number of \[Y\text{ }=\text{ }6\text{ }+\text{ }8\text{ }=\text{ }14\]

Atomic number = Number of protons

The atomic number of X= 6 = Atomic number of Y

These two atomic species X and Y have the same atomic number, but different mass numbers. Hence, they are isotopes.

14. For the following statements, write T for ‘True’ and F for ‘False’.

a). J.J. Thomson proposed that the nucleus of an atom contains only nucleons.

Ans: False

b). A neutron is formed by an electron and a proton combining together. Therefore, it is neutral.

c). The mass of an electron is about 1/2000 times that of the proton.

Ans: True

d). An isotope of iodine is used for making tincture iodine, which is used as a medicine.

15. Rutherford’s alpha-particle scattering experiment was responsible for the discovery of

Atomic nucleus

Ans: a) Atomic Nucleus

16. Isotopes of an element have

The same physical properties

Different chemical properties

Different number of neutrons

Different atomic numbers

Ans: c) Different numbers of neutrons.

Isotopes are atoms of the same element having the same atomic number, but different mass numbers.

17. Number of valence electrons in $\mathrm{Cl}^{-1}$ ion is:

Ans: Atomic number of $\mathrm{Cl}$ = $17$

Electronic configuration of $\mathrm{Cl}$ = \[2,\text{ }8,\text{ }7\]

Electronic configuration of $\mathrm{Cl}^{-1}$ ion \[=\text{ }2,\text{ }8,\text{ }8\]

Thus, the number of valence electrons in $\mathrm{Cl}^{-1}$ ion = $8$

18. Which one of the following is a correct electronic configuration of sodium?

Ans: Atomic number of sodium = = Number of electrons

So, electronic configuration of sodium = 2, 8, 1.

19. Complete the following table.

NCERT Solutions for Class 9 Science Chapter 4 - Structure of The Atom

You can opt for Chapter 4 - Structure of Atom NCERT Solutions for Class 9 Science PDF for Upcoming Exams and also You can Find the Solutions of All the Maths Chapters below.

Summary of Structure of the Atom Class 9

The 4 th chapter will deliver a constructed concept of how an atom is subdivided into subatomic particles. It will also tell you how scientists proved the existence of subatomic particles within an atom. The consecutive development of theories will make you understand how an atom stabilizes its charges. It is a fascinating chapter to learn and prepare a foundation to rely on. You will need these new concepts to study more advanced chapters in the future. To make it easier, you need to follow the Structure of The Atom Class 9 NCERT Solutions available here to find the right answers to all the questions.

Study the chapter well and focus on what the units are telling us to follow. Develop your concepts accordingly and find out new scientific facts about an atom and its subatomic particles. Proceed with proper attention. Once you finish a unit, solve the exercise, and judge your understanding of the concepts. You can also use NCERT Solutions for Class 9 Science Chemistry Chapter 4 as a platform to judge your base. Follow the best answers given in the NCERT Solutions for Class 9 Science Structure of The Atom to discover how to frame the perfect solution and score well in an exam.

How Should you Proceed with CBSE Class 9 Science Chapter 4 Solutions?

Here is what you need to do to study the new concepts of Class 9 Science Chapter 4.

1. Read the Chapter Thoroughly

The first step is to read the units of Ch 4 Science Class 9 properly and understand the new concepts. You must only proceed to the next unit when you are done with the previous one.

2. Answers the Exercise Questions

The next step is to find the questions in the unit exercise. Answer the questions on your own first. Seek the right answers from the NCERT Solutions Class 9 Science Structure of The Atom so that you can find out whether your answers were to the point or not.

3. Follow the format of NCERT Solutions for Class 9 Science Chapter 4 Structure of the Atom

When you are satisfied with your concept development, you need to follow the format used by the experts in NCERT Solutions for Class 9th Science Chapter 4 Structure of The Atom. The answers are based on the CBSE format. They are precise and easy to understand.

4. Focus on the Concept Delivery in NCERT Solutions for Class 9 Science Chapter Structure of The Atom

You will be able to understand how the concepts are focused and used to answer the questions in the NCERT Solutions Class 9 Science Chapter 4 Structure of The Atom. Just follow it and impress the examiner to score better.

Why Use the NCERT solution for Class 9 Science Chapter 4 from Vedantu?

Download Structure of The Atom Class 9 NCERT Solutions PDF for free from the portal. You can use it offline to study the different conceptual answers framed for the respective exercises. Vedantu experts have formed these answers for your convenience. You can save your precious time and concentrate on learning this chapter properly.

Advantages of NCERT Solutions for Class 9 Science Chapter 4

The following are some of the key benefits of practising the NCERT Solutions for Class 9 Science Chapter 4 “Structure of Atom.”

Expert Curated: Revision notes crafted by subject experts, ensuring coverage of all crucial topics for comprehensive understanding.

Simple and Precise Format: Notes presented in a straightforward, precise, and easy-to-understand format, promoting clarity and efficient revision.

Inclusion of Important Diagrams: The revision notes feature a list of key diagrams, enhancing conceptual understanding and aiding visual learners.

Illustrative Examples: Concepts are reinforced with examples, providing practical applications to enhance comprehension of the underlying theories.

NCERT Solutions for Class 9 Science Chapter 4, "Structure of the Atom," comprehensively addresses all exercises, providing a detailed understanding of crucial topics. The solutions cover fundamental concepts such as the discovery of electrons, protons, and neutrons, Bohr's model, and the modern atomic model. By offering step-by-step explanations and illustrations, this resource ensures clarity in comprehension. For further assistance, the downloadable NCERT solutions PDF serves as a valuable aid in exam preparation. We trust that this discussion has effectively addressed your queries, offering a strong foundation to master the aspects of atomic structure.

We wish you all the very best for the upcoming examinations!

NCERT Solutions for Class 9 Science

Chapter 1 - Matter in Our Surroundings

Chapter 2 - Is Matter Around us Pure

Chapter 3 - Atoms and Molecules

Chapter 4 - Structure of Atom

Chapter 5 - The Fundamental Unit of Life

Chapter 6 - Tissues

Chapter 7 - Diversity in Living Organisms

Chapter 8 - Motion

Chapter 9 - Force and Laws of Motion

Chapter 10 - Gravitation

Chapter 11 - Work and Energy

Chapter 12 - Sound

Chapter 13 - Why do We Fall ill

Chapter 14 - Natural Resources

Chapter 15 - Improvement in Food Resources

Along with this, students can also view additional study materials provided by Vedantu, for Class 9

NCERT Solutions For Class 9

Revision Notes for Class 9

CBSE Class 9 Syllabus

FAQs on NCERT Solutions for Class 9 Science Chapter 4 - Structure Of The Atom

1. Why use Solutions for Class 9 Science Chapter 4 PDF?

You can start studying Chapter 4 beforehand and prepare the syllabus for an exam efficiently. Rely on the precise answers and build your concept to stay ahead of the class. Download the NCERT Solutions for Class 9 Science Chapter 4 PDF for free and start your preparation today.

2. Why Should you Prefer the Answers in NCERT Solutions for Class 9 Science Ch 4?

These answers are prepared by the experienced teachers following the latest CBSE guidelines so that you can score well in the exam.

3. How NCERT Solutions for Class 9 Chemistry Chapter 4 can Help You?

The format used in the answers in Structure of The Atom Class 9 NCERT Solutions will help you follow the guidelines. You will be able to give the right answers by maintaining the word count and score better.

4. What is the structure of an atom?

The structure of an atom consists of three main particles - protons, electrons, and neutrons. The centre of an atom is called the nucleus, which consists of the positively charged protons and the no-charge neutrons. Outside the nucleus, there are electron shells that contain negatively charged electrons. Based on the number of protons and electrons, each atom shows its properties. For similar solutions, download the NCERT Solutions Class 9 Science Chapter 4 available on Vedantu website (vedantu.com) and the app.

5. Who discovered atom according to Chapter 4 of Class 9 Science?

It was John Dalton who gave us the first modern theory of an atom and its structure. According to Dalton, atoms are indivisible and indestructible units that form matter. Atoms present in the same element are similar or identical. Atoms of different elements can vary in mass and size. Compounds are created by combining different atoms. And, the rearrangement of atoms in the presence of a reactant can cause a chemical reaction and produce a chemical product.

6. Write the names of three subatomic parts of the atom.

The smallest unit present in any matter is an atom. It contains protons, electrons, and neutrons inside it and these are the three subatomic parts of an atom. While protons are positively charged, electrons are negatively charged and neutrons are neutral or no charge. To know more about the topic in detail, you can visit Vedantu website and mobile app.

7. What is Bohr's model according to Chapter 4 of Class 9 Science?

According to Bohr’s Model of Atom, an atom consists of a nucleus that is heavily charged (positive) due to the presence of protons. All the mass of an atom is constituted in the nucleus. Outside the nucleus, there are definiṯe orbits or energy levels that are circular - these consist of electrons. Every orbit has an exact energy amount. Whenever an electron jumps from one orbit to another, it causes a change in energy. To study more about atoms, students can download the NCERT solutions free of cost from the Vedantu website.

8. What is Thomson’s model of an atom?

According to J.J Thompson, the model of an atom is like a Christmas pudding. It has a positive sphere, in which, embedded are the electron particles like currants on a Christmas pudding. He believed that the positive and negative charges in an atom were equal and therefore, an atom was electrically neutral. But, we know that with experiments conducted by scientists later it was proved that JJ Thompson’s model of an atom was not correct.

NCERT Solutions for Class 9

NCERT Solutions for Class 9 Science Chapter 4 Structure of the Atom

NCERT Solutions for Class 9 Science Chapter 4 Structure of the Atom in Hindi and English Medium prepared for new session 2024-25. Class 9 Science chapter 4 is modified and revised as per the new rationalised NCERT textbooks issued for academic year 2024-25.

Class 9 Science Chapter 4 Question Answers

Class 9 Science Chapter 4 Exercises
Class 9 Science Chapter 4 Intext Questions
Class 9 Science Chapter 4 Extra Questions
Class 9 Science Chapter 4 Hindi Medium
Class 9 Science Chapter 4 Notes in English
Class 9 Science Chapter 4 Notes in Hindi
Class 9 Science Chapter 4 NCERT Book
Class 9 Science NCERT Solutions
Class 9 all Subjects NCERT Solutions

NCERT Class 9 Science textbook, Chapter 4 Structure of the Atom delves into the structure and components of atoms, providing insight into the fundamental building blocks of matter. The main topics covered in Chapter 4 are the concept of the atom as the basic unit of matter, Dalton’s Atomic Theory that is a brief overview of Dalton’s atomic theory and its postulates. Here we will study about Charged Particles in Matter which provides the explanation of charged particles in matter, including electrons, protons, and neutrons.

Distribution of Electrons in Different Orbits (Shells) Class 9 students learn in chapter 4 about explanation of electron distribution in shells or energy levels and introduction to the K, L, M, and N shells. It also explains the definition of valency and its significance, determining valency based on electron distribution. Here, we learn about Atomic Number and Mass Number with explanation of atomic number and its significance, definition of mass number and how it is determined. Class 9 science chapter 4 explores about the definition of isotopes and examples, explanation of isotopic notation.

A recap of the main concepts and ideas presented in Chapter 4 Structure of the Atom, provides a foundational understanding of the structure and components of atoms. It introduces students to the historical development of atomic models and sets the stage for further exploration of atomic and molecular structures in subsequent chapters and classes.

Preparing for NCERT Class 9 Science Chapter 4 Structure of the Atom, requires a proper approach to understanding the fundamental concepts related to atomic structure. Here are some steps and planning strategies for students to prepare this chapter 4 of 9th science effectively. First of all, read the Chapter Thoroughly, begin by reading the chapter carefully from the NCERT textbook. Pay attention to definitions, examples, and key points. While reading, take detailed notes on important concepts, definitions, and key terms.

To make science easy, summarize the main ideas of each section. Understand the historical development of atomic models, including Dalton’s atomic theory, J.J. Thomson’s experiments, Rutherford’s gold foil experiment, and Bohr’s model. Know the key contributions of these scientists. Study the components of an atom, including electrons, protons, and neutrons. Understand their properties, locations, and charges. Learn about Bohr’s model of the hydrogen atom, including the concept of energy levels or orbits and how it explains spectral lines.

Class IX Science chapter 4 Exercise and Intext question answers in PDF format to free download. Class 9 UP Board students also get here UP Board Solutions. Class 9 Science chapter 4 Intext questions given on Page 43 or Page 49 or Page 50 or Page 52 or Page 53 and Exercises in English Medium are available.

You can download these solutions from Page 53 ke Uttar or Page 56 ke Uttar or Page 57 ke Uttar or Page 58 ke uttar or Page 59 ke Uttar or Page 60 ke Uttar and Abhyaas ke Uttar to study online or in PDF file format. NCERT Solutions and Offline Apps for all other subjects based on latest CBSE Syllabus are also available to download.

Electron Distribution and Valency Understand how electrons are distributed in different shells or energy levels (K, L, M, N). Learn the maximum number of electrons each shell can hold. Know the definition of valency and how it relates to electron distribution. Practice determining the valency of elements based on their electron configuration. Learn how to calculate the number of protons, electrons, and neutrons in an atom. Isotopes: Understand isotopic notation.

Practice solving numerical problems related to atomic structure, atomic number, mass number, and electron distribution. Work through exercises and examples in the textbook. Utilize diagrams and visual aids in the chapter to help understand atomic structures and models. Supplement your learning with online resources, videos, and interactive simulations related to atomic structure. These can provide additional clarity. Group study can offer different perspectives and help reinforce your understanding.

Regularly revise your notes and the key points of the chapter 4 in 9th science. Repetition is key to retaining information. Closer to your exams, practice solving sample papers and previous year’s question papers to familiarize yourself with the exam pattern and practice time management. If you have doubts or find certain topics challenging, don’t hesitate to seek help from your teacher or classmates. Clarify your doubts as soon as possible. By following these planning strategies and staying organized, you can effectively prepare for NCERT Class 9 Science Chapter 4 and build a strong foundation in atomic structure and chemistry concepts.

Extra Questions on 9th Science Chapter 4

Is atomic number of an atom always equal to the number of electrons.

No, it is the case when the atom has no charge. In case of cation (positively charged), atomic number is more than the number of electrons and in case of anion (negatively charged), it is less than the number of electrons.

Nucleus of an atom has positive charge on it. Establish.

This can be established on the basis of Rutherford scattering experiment. Since some alpha particles were repelled by the nucleus of the atom, it is expected to have the same charge as on alpha particles. Therefore, nucleus of an atom has positive charge.

Were neutrons known at the time Rutherford performed the scattering experiment?

No, these were discovered later on by Chadwick in 1931 whereas scattering experiment was performed by Rutherford in 1911.

Why are isotopes of an element chemically similar?

Isotopes of an elements have same number of electrons and therefore, same value shell electronic distribution. Since the chemical properties of the atoms are related to valence shell configurations, the isotopes are chemically similar.

Why do elements which exist as isotopes have fractional atomic masses?

The different isotopes of an element differ in their mass number as well as atomic masses. In order to represent the atomic mass of the element, we have to consider average of the atomic masses of the different isotopes and also the ratio in which these are present. In most of the cases, the average comes out to be in fraction. Therefore, these elements have fractional atomic masses.

Why is a proton not a universal particle like electron?

A proton is the positively charged residue left when hydrogen gas is enclosed in the in the discharge tube. For the other gases, the positive residues formed contain different number of protons. Therefore, proton is not a universal particle like electron.

Tiwari Academy plays a significant role in helping students prepare for NCERT Class 9 Science Chapter 4. Here’s how Tiwari Academy can assist students in their preparation for this chapter. It provides detailed solutions to all the questions and exercises in the NCERT Class 9 Science textbook for Chapter 4. These solutions can help students understand how to approach and solve different types of problems related to the structure of atoms.

Class 9 Science Chapter 4 Structure of the Atom

Important Questions on 9th Science Chapter 4

What are the limitations of j.j. thomson’s model of the atom.

According to J.J. Thomson’s model of an atom, an atom consists of a positively charged sphere with electrons embedded in it. However, it was later found that the positively charged particles reside at the center of the atom called the nucleus, and the electrons revolve around the nucleus.

What are the limitations of Rutherford’s model of the atom?

According to Rutherford’s model of an atom, electrons revolve around the nucleus in fixed orbits. But, an electron revolving in circular orbits will not be stable because during revolution, it will experience acceleration. Due to acceleration, the electrons will lose energy in the form of radiation and fall into the nucleus. In such a case, the atom would be highly unstable and collapse.

Define valency by taking examples of silicon and oxygen.

The valency of an element is the combining capacity of that element. The valency of an element is determined by the number of valence electrons present in the atom of that element. If the number of valence electrons of the atom of an element is less than or equal to four, then the valency of that element is equal to the number of valence electrons. For example, the atom of silicon has four valence electrons. Thus, the valency of silicon is four. On the other hand, if the number of valence electrons of the atom of an element is greater than four, then the valency of that element is obtained by subtracting the number of valence electrons from eight. For example, the atom of oxygen has six valence electrons. Thus, the valency of oxygen is (8 − 6) i.e., two.

Explain Atomic number with examples.

Atomic number: The atomic number of an element is the total number of protons present in the atom of that element. For example, nitrogen has 7 protons in its atom. Thus, the atomic number of nitrogen is 7.

What do you understand by isobars?

Isobars: They are atoms of different elements having same mass number but different atomic number. For example calcium, atomic number 20 and argon, atomic number 18. The number of electrons in these atoms is different, but the mass number of both these elements is 40. That is, the total number of neutrons is the same in the atoms of this pair of elements.

If Z = 3, what would be the valency of the element? Also, name the element.

By Z = 3, we mean that the atomic number of the element is 3. Its electronic configuration is 2, 1. Hence, the valency of the element is 1 (since the outermost shell has only one electron). Therefore, the element with Z = 3 is lithium.

NCERT Solutions for Class 9 Science Chapter 4 Structure of the Atom Intext Questions and chapter end exercise question answers are given below to free download. All the solutions are free to download without any registrations or login. We have updated all the contents on the basis of user’s suggestions and Feedback received from last academic session.

The Tiwari Academy website and apps offer explanations and videos that break down complex concepts in the chapter. Visual aids and clear explanations can help students grasp difficult topics more easily. It also provide historical context and explanations for the development of atomic models, making it easier for students to understand the evolution of atomic theory. The platform offer visual representations and interactive simulations of atomic structures, which can enhance students’ understanding of the arrangement of electrons, protons, and neutrons within an atom.

Questions related to class 9 science chapter 4, atomic structure and atomic models are frequently included in Class 9 Science examinations. Students can expect to see questions about atomic components, electron distribution, atomic number, and mass number in their exams. The chapter covers the historical development of atomic models, including Dalton’s atomic theory, J.J. Thomson’s experiments, Rutherford’s gold foil experiment, and Bohr’s model. Understanding the history of atomic theory is often tested in exams.

Question 1: An electron is regarded as a universal particle. Explain. Answer 1: The value of charge (e) and mass (m) of the electron always remain the same whatever may be the source of their emission. In the discharge tube, the electrons may be emitted either from the cathode or form the gas enclosed in the discharge tube. Whatever may be the metal which forms the cathode or the gas present in the discharge tube, these values remain the same. Therefore, electron is regarded as a universal particle.

Question 2: Why do the element helium, neon and argon have zero valency? Answer 2: Helium has two electrons in its only energy shell (K-shell). The other two elements have eight electrons in their valence shells. Since these are the maximum number of electrons which the atoms of these elements can have therefore, they do not have any urge or desire to take part in chemical combination. These elements are known as zero valent elements. They have therefore, valency equal to zero.

Class 9 Science chapter 4 bridges the gap between chemistry and physics by introducing concepts related to atomic structure. It sets the stage for students to explore topics like the periodic table, chemical bonding, and atomic physics in later classes. Knowledge of atomic structure is relevant to various scientific fields, including chemistry, physics, and materials science. Exams include questions that require students to apply their understanding of atomic structure to real-world scenarios. A strong foundation in Chapter 4 is, therefore, essential for success in future science studies.

Finally, the NCERT Class 9 Science Chapter 4, Structure of the Atom, is important not only for scoring well in exams but also for laying the groundwork for a deeper understanding of chemistry and physics concepts. Students should dedicate time and effort to comprehensively learn the concepts presented in this chapter to ensure success in their science studies.

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NCERT Solutions for Class 9 Science Chapter 4 Structure of the Atom

23rd December 2023

NCERT Solutions for Class 9 Science (Chemistry) Chapter 4 Structure of the Atom provides detailed answers for all in-text and exercise Questions. These solutions contain an in-depth explanation of each topic involved in the chapter. All these solutions are prepared by expert teachers and updated for the current academic session.

NCERT Solutions for Class 9 Science (Chemistry) Chapter 4 Structure of the Atom Pure help students to understand the fundamental concepts given in class 9 Science textbook. We have prepared the answers to all the questions in an easy and well-structured manner. It helps students to grasp the chapter easily.

CBSE Class 9 Science Structure of the Atom Intext Questions (Solved)

PAGE NO – 39

Question 1: What are canal rays?

Answer: Canal rays are positively charged radiations. These rays consist of positively charged particles known as protons. They were discovered by Goldstein in 1886.

Question 2: If an atom contains one electron and one proton, will it carry any charge or not?

Answer: If an atom contains one electron and one proton, it will not carry any net charge. This is because a proton has a positive charge and an electron has a negative charge, and these two charges are equal in magnitude but opposite in sign. In such an atom, the positive charge of the proton and the negative charge of the electron will cancel each other out, resulting in a neutral overall charge. An example of such an atom is hydrogen, which typically has one proton and one electron in its most common form.

PAGE NO. 41

Question 1: On the basis of Thomson’s model of an atom, explain how the atom is neutral as a whole.

Answer: According to Thomson’s model of the atom, an atom consists of both negatively and positively charged particles. The negatively charged particles are embedded in the positively charged sphere. These negative and positive charges are equal in magnitude. Thus, by counterbalancing each other’s effect, they make an atom neutral.

According to Thomson’s model, an atom is neutral because it contains an equal amount of positive and negative charges that balance each other out. In this model, the atom is like a positively charged sphere with negatively charged electrons embedded in it. The positive charge is spread out over the entire sphere, and the electrons are placed within this sphere. Since the number of negative charges (electrons) equals the number of positive charges in the sphere, the overall charge of the atom is neutral. This balance of equal and opposite charges ensures that the atom does not have a net charge.

Question 2: On the basis of Rutherford’s model of an atom, which subatomic particle is present in the nucleus of an atom?

Answer: On the basis of Rutherford’s model of an atom, protons (positively-charged particles) are present in the nucleus of an atom.

Question 3: Draw a sketch of Bohr’s model of an atom with three shells.

NCERT Solutions for Class 9 Science Chapter 4 Structure of the Atom image 1

Question 4: What do you think would be the observation if the α-particle scattering experiment is carried out using a foil of a metal other than gold?

Answer: If the α-scattering experiment is carried out using a foil of metal rather than gold, there would be no change in the observation. In the α-scattering experiment, a gold foil was taken because gold is malleable and a thin foil of gold can be easily made. It is difficult to make such foils from other metals.

Question 1: Name the three sub-atomic particles of an atom.

Answer: The three sub-atomic particles of an atom are:

Protons
Electrons, and

Question 2: Helium atom has an atomic mass of 4 u and two protons in its nucleus. How many neutrons does it have?

Answer: Helium atom has two neutrons. The mass of an atom is the sum of the masses of protons and neutrons present in its nucleus.

Since helium atom has two protons, mass contributed by the two protons is (2 × 1) u = 2 u. Then, the remaining mass (4 − 2) u = 2 u is contributed by 2u /1u = 2 neutrons.

PAGE NO. 42

Question 1: Write the distribution of electrons in carbon and sodium atoms?

Answer: The total number of electrons in a carbon atom is 6. The distribution of electrons in carbon atom is given by:

Or, we can write the distribution of electrons in a carbon atom as 2, 4. The total number of electrons in a sodium atom is 11. The distribution of electrons in sodium atom is given by:

Or, we can write distribution of electrons in a sodium atom as 2, 8, 1.

Question 2: If K and L shells of an atom are full, then what would be the total number of electrons in the atom?

Answer: The maximum number of electrons that can occupy K and L-shells of an atom are 2 and 8 respectively. Therefore, if K and L-shells of an atom are full, then the total number of electrons in the atom would be (2 + 8) = 10 electrons.

PAGE NO. 43

Question 1: How will you find the valency of chlorine, sulphur and magnesium?

Answer: If the number of electrons in the outermost shell of the atom of an element is less than or equal to 4, then the valency of the element is equal to the number of electrons in the outermost shell.

On the other hand, if the number of electrons in the outermost shell of the atom of an element is greater than 4, then the valency of that element is determined by subtracting the number of electrons in the outermost shell from 8.

The distribution of electrons in chlorine, sulphur, and magnesium atoms are 2, 8, 7; 2, 8, 6 and 2, 8, 2 respectively. Therefore, the number of electrons in the outermost shell of chlorine, sulphur, and magnesium atoms are 7, 6, and 2 respectively.

Thus, The valency of chlorine = 8 −7 = 1 The valency of sulphur = 8 − 6 = 2 The valency of magnesium = 2

Question 1: If number of electrons in an atom is 8 and number of protons is also 8, then (i) what is the atomic number of the atom and (ii) what is the charge on the atom?

Answer: (i) The atomic number is equal to the number of protons. Therefore, the atomic number of the atom is 8.

(ii) Since the number of both electrons and protons is equal, therefore, the charge on the atom is 0.

Question 2: With the help of Table 4.1, find out the mass number of oxygen and sulphur atom.

Answer: Mass number of oxygen = Number of protons + Number of neutrons = 8 + 8 = 16

Mass number of sulphur = Number of protons + Number of neutrons = 16 +16 = 32

PAGE NO. 45

Question 1: For the symbol H, D and T tabulate three sub – atomic particles found each of them.

Question 2: Write the electronic configuration of any pair of isotopes and isobars.

Answer: Isotopes: Isotopes are atoms which have the same number of protons but the number of neutrons differs. This leads to the variation in mass number too.

Two isotopes of carbon are 6 𝐶 12 and 6 𝐶 14 The electronic configuration of 6 𝐶 12 is 2, 4. The electronic configuration of 6 𝐶 14 is 2, 4. [Isotopes have same electronic configuration]

Isobars: Isobars are atoms which have the same mass number but differ in the atomic number. Electronic configuration of an isobar pair is as follows,

29 Ca 40 and 8 𝐴𝑟 40 are a pair of isobars of calcium. The electronic configuration of 29 Ca 40 is 2, 8, 8, 2 The electronic configuration of 18 𝐴𝑟 40 is 2, 8, 8. [Isobars have different electronic configuration]

NCERT Class 9 Science Structure of the Atom Exercise Questions (Solved)

Question 1: Compare the properties of electrons, protons and neutrons.

Question 2: What are the limitations of J.J. Thomson’s model of the atom?

Answer: J.J. Thomson’s model of the atom, known as the “plum pudding model,” had a few key limitations:

1. According to J.J. Thomson’s model of an atom, an atom consists of a positively charged sphere with electrons embedded in it. However, later Rutherford’s gold foil experiment showed that the positively charged particles reside at the center of the atom called the nucleus, and the electrons revolve around the nucleus.

2. Thomson’s model was unable to explain many chemical properties of elements, such as why atoms combine in fixed ratios to form compounds.

3. It didn’t clearly distinguish between the nucleus and the rest of the atom, and couldn’t explain why atoms are stable.

Question 3: What are the limitations of Rutherford’s model of the atom?

Answer: According to Rutherford’s model of an atom, electrons revolve around the nucleus in fixed orbits. But, an electron revolving in circular orbits will not be stable because, during the revolution, it will experience acceleration. Due to acceleration, the electrons will lose energy in the form of radiation and fall into the nucleus. In such a case, the atom would be highly unstable and collapse.

Question 4: Describe Bohr’s model of the atom.

Answer: Bohr’s model of the atom Niels Bohr proposed the following postulates regarding the model of the atom.

Only certain orbits known as discrete orbits of electrons are allowed inside the atom.
While revolving in these discrete orbits, the electrons do not radiate energy. These discrete orbits or shells are shown in the following diagram.

NCERT Solutions for Class 9 Science Chapter 4 Structure of the Atom image 2

The first orbit (i.e., for n = 1) is represented by letter K. Similarly, for n = 2, it is L − shell, for n = 3, it is M − shell and for n = 4, it is N − shell. These orbits or shells are also called energy levels.

Question 5: Compare all the proposed models of an atom given in this chapter.

Question 6: Summarize the rules for writing of distribution of electrons in various shells for the first eighteen elements.

Answer: The rules for writing of the distribution of electrons in various shells for the first eighteen elements are given below:

(i) The maximum number of electrons that a shell can accommodate is given by the formula ‘2n 2 ‘, where ‘n’ is the orbit number or energy level index (n = 1, 2, 3…). Now, Maximum number of electrons in different shells are: K shell n = 1: 2n 2 = 2(1) 2 = 2 L shell n = 2: 2n 2 = 2(2) 2 = 8 M shell n = 3: 2n 2 = 2(3) 2 = 18 N shell n = 4: 2n 2 = 2(4) 2 = 32

(ii) The outermost orbit can be accommodated by a maximum number of 8 electrons.

(iii) Shells are filled with electrons in a step-wise manner i.e., the outer shell is not occupied with electrons unless the inner shells are completely filled with electrons.

Question 7: Define valency by taking examples of silicon and oxygen.

Answer: Valency is the measure of the ability of an atom to combine with other atoms. It is determined by the number of electrons an atom can lose, gain, or share to become stable.

Example with Silicon : Silicon has 4 electrons in its outermost shell. It can share these 4 electrons with other atoms to complete its outer shell, typically holding 8 electrons. So, the valency of silicon is 4, as it can form bonds by sharing 4 electrons.
Example with Oxygen : Oxygen has 6 electrons in its outer shell. It needs 2 more electrons to complete its shell. So, it can either gain 2 electrons or share 2 electrons with other atoms. Therefore, the valency of oxygen is 2.

Question 8. Explain with examples: (i) Atomic number (ii) Mass number, (iii) Isotopes and (iv) Isobars. Give any two uses of isotopes.

(i) Atomic number: The atomic number of an element is the total number of protons present in the atom of that element. For example, nitrogen has 7 protons in its atom. Thus, the atomic number of nitrogen is 7.

(ii) Mass number: The mass number of an element is the sum of the number of protons and neutrons present in the atom of that element. For example, the atom of boron has 5 protons and 6 neutrons. So, the mass number of boron is 5 + 6 = 11.

(iii) Isotopes: They are atoms of the same element and have same atomic number but different mass number/atomic mass. For example: C 12 and 6 C 14

(iv) Isobars: They are atoms of different elements having same mass number but different atomic number. For example calcium, atomic number 20 and argon, atomic number 18. The number of electrons in these atoms is different, but the mass number of both these elements is 40. That is, the total number of neutrons is the same in the atoms of this pair of elements.

Two uses of isotopes are as follows:

An isotope of uranium is used as a fuel in nuclear reactors.
An isotope of cobalt is used in the treatment of cancer.

Question 9: Na has completely filled K and L shells. Explain.

Answer: Na has atomic number 11, so its electronic configuration is = 2, 8, 1 Sodium atom (Na) looses 1 electron to become stable and form Na + ion. so its electronic configuration is = 10 = 2, 8. The above configuration indicates completely filled K, L shells.

Question 10: If bromine atom is available in the form of, say, two isotopes 35 𝐵𝑟 79 (49.7%) and 35 𝐵𝑟 81 (50.3%), calculate the average atomic mass of bromine atom.

Answer: The average atomic mass of bromine

NCERT Solutions for Class 9 Science Chapter 4 Structure of the Atom image 3

Question 11. The average atomic mass of a sample of an element X is 16.2 u. What are the percentages of isotopes 16 8 X and 18 8 X in the sample?

NCERT Solutions for Class 9 Science Chapter 4 Structure of the Atom image 4

Question 12: When 90% is the X-16 sample so for X-18 sample % = 100-90=10% If Z = 3, what would be the valency of the element? Also, name the element.

Answer: By Z = 3, we mean that the atomic number of the element is 3. Its electronic configuration is 2, 1. Hence, the valency of the element is 1 (since the outermost shell has only one electron). Therefore, the element with Z = 3 is lithium.

Question 13: Composition of the nuclei of two atomic species X and Y are given as under

Give the mass numbers of X and Y. What is the relation between the two species?

Answer: Mass number of X = Number of protons + Number of neutrons = 6 + 6 = 12

Mass number of Y = Number of protons + Number of neutrons = 6 + 8 = 14

These two atomic species X and Y have the same atomic number, but different mass numbers. Hence, they are isotopes.

Question 14. For the following statements, write T for true and F for false. (a) J.J. Thomson proposed that the nucleus of an atom contains only nucleons. (b) A neutron is formed by an electron and a proton combining together. Therefore it is neutral. (c) The mass of an electron is about 1/2000 times that of proton. (d) An isotope of iodine is used for making tincture iodine, which is used as a medicine.

Solution: (a) False (b) False (c) True (d) False

Put a tick(✓) against correct choice and cross(x) against wrong choice in questions 15, 16 and 17.

Question 15. Rutherford’s alpha-particle scattering experiment was responsible for the discovery of (a) Atomic nucleus (b) Electron (c) Proton (d) Neutron

Answer: (a) Atomic nucleus

Question 16. Isotopes of an element have (a) The same physical properties (b) Different chemical properties (c) Different number of neutrons (d) Different atomic numbers.

Answer: (c) Different number of neutrons

Question 17. Number of valence electrons in Cl − ion are: (a) 16 (b) 8 (c) 17 (d) 18

Answer: (b) 8

Electronic distribution of Cl is K-2, L-8, M-7. Valence electrons are 7, hence chlorine gains one electron for the formation of Cl – . Therefore, its valency is 8.

Question 18. Which one of the following is a correct electronic configuration of Sodium? (a) 2, 8 (b) 8, 2, 1 (c) 2, 1, 8 (d) 2, 8, 1

Answer: (d) 2, 8, 1

Question 19: Complete the following table.

NCERT Solutions for Class 9 Science Chapter 4 Structure of the Atom image 5

Answer: The following table depicts the missing data: Atomic number(Z) =Number of protons Mass number = Number of neutrons + atomic number (or) Mass number(A) = Number of neutrons + number of neutrons

NCERT Solutions for Class 9 Science Chapter 4 Structure of the Atom

Chapter 4 Structure of Atom NCERT Solutions for Class 9 Science

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Extra Questions for Class 9 Science Chapter 4 Structure of the Atom

Extra questions for Class 9 Science Chapter 4 Structure of the Atom with answers is given below. Our subject expert prepared these solutions as per the latest NCERT textbook. These questions will be helpful to revise the all topics and concepts. CBSE Class 9 extra questions are the most simple and conceptual questions that are prepared by subject experts for the students to study well for the final exams. By solving these extra questions, students can be very efficient in their exam preparations.

Structure of the Atom Class 9 Science Extra Questions and Answers

Very short answer questions.

1: Draw the atomic structure of hydrogen atom. Answer:

Extra Questions for Class 9 Science Chapter 4 Structure of the Atom 1

2: Why are some elements chemically inert? Answer: Because their outermost shell is completely filled.

3: Why is atom electrically neutral? Answer: It has same number of protons and electrons, (positive charge = negative charge).

4: What is the charge and mass of a-particles? Answer: Charge is + 2 Mass is 4 a.m.u.

5: What are valence electrons? Answer: Electrons present in the outermost shell of an atom are called valence electrons.

6: An atom has atomic number 12, what is its valency and name the element? Answer: Atomic number = 12 ∴ Protons = Electrons = 12 Electrons Configuration = K L M -2 8 2 ∴ Valency = 2 Element is magnesium.

7: Find the number of neutrons in 27 13 X. Answer: Mass number = 27 ∴ p + n = 27 p = 13, (Atomic No. = Number of protons) ∴ 13 + n = 27 ∴ n = 14 ∴ Neutron =14

8: Where is the mass of atom is concentrated? Answer: Mass of an atom is concentrated in nucleus.

9: Name two elements with same number of protons and neutrons? Answer: Carbon (Protons = Neutrons = 6) Oxygen (Protons = Neutrons = 8)

10: Draw the atomic structure of sodium atom. Answer:

Extra Questions for Class 9 Science Chapter 4 Structure of the Atom 2

11: Name the isotope used for treatment of cancer. Answer: Isotope of cobalt. 12: AZX What does this symbol represent? Answer: X → Symbol of element A → Mass number Z → Atomic number

13: Can the value of ‘Z’ be same for two different atoms? Answer: No, (Z = atomic number), two different atoms cannot have same atomic number.

14: Can the value of A’ be same for two different atom? Answer: Yes, it can be e.g. Ca and Ar has A-40 (i.e., mass number).

Short Answer Type Questions

1: Name the scientist who discovered protons and neutrons in an atoms. Answer: Protons were discovered by E. Goldstein in 1866 and neutrons were discovered by J, Chadwick in 1932.

2: What is the contribution of Bohr and Bury together in the structure of atom’s explanation? Answer: Both Bohr and Bury gave the distribution of electrons into different atoms by giving the formula 2n 2 , where n = shell number.

3: Draw the atomic structure of (i) an atom with same number of sub-atomic particles, (ii) an atom with same number of electrons in L and M shell.

Answer: (i) An atom with same number of sub-atomic particles is He No. of protons = 2 No. of electrons = 2 No. of neutrons = 2

Extra Questions for Class 9 Science Chapter 4 Structure of the Atom 3

(ii) An atom with L and M shell filled → K L M- 2 8 8

Extra Questions for Class 9 Science Chapter 4 Structure of the Atom 4

4: What is an octate? Why would atoms want to complete their octate?

Answer: When the outermost shell of an atom i.e., L, M or N are completely filled with 8 electrons in the shell, it is said an octate. Atoms would want to complete their octate because they want to become stable.

5: Find the valency of 14 7 N and 35 17 Cl.

Answer: The atomic number of nitrogen = 7, No. of protons = 7, No. of electrons = 7 Electronic configuration = K L M = 2 5 – Valency = 3 Because either it will gain three electrons or share 3 electrons to complete its octate. The atomic number of chlorine = 17, p = 17, e=17 Electronic configuration = K L M= 2 8 7 Valency = 1 Because it will gain 1 electron to complete its octate.

Extra Questions for Class 9 Science Chapter 4 Structure of the Atom 5

8: What are nucleons? What is the name given to those atoms which have same number of nucleons in it?

Answer: Protons and neutrons present in the nucleus are called nucleons Isobaric elements have same number of nucleons in it.

9: Give the difference between three sub-atomic particles.

Answer: Three sub-atomic particles are electron, proton and neutron

Extra Questions for Class 9 Science Chapter 4 Structure of the Atom 6

10. Give the names of three atomic species of hydrogen. Answer: Three atomic species of hydrogen are:

11: Atomic Mass exists as whole number, why do we write the atomic mass of chlorine as 35.5 u.

Answer: Chlorine has two isotopes and the mass of an atom is taken as the average mass of all the naturally occurring atoms of that element. This is obtained by knowing the percentage of each isotopic from and then the average mass is calculated Cl = 35 – 75% and Cl = 37 – 25% = 35.5 u

Extra Questions for Class 9 Science Chapter 4 Structure of the Atom 7

12: Give difference between isotopes, and isobars. Answer:

13: Number of protons and electrons are same in an atom. Then why is it wrong to say that atomic number of an atom is equal to its number of electrons.

Answer: Atomic number ≠ Number of electrons, although number of protons = number of electrons because the electron’s number can change in an atom by loss, or gain of it. But the proton’s number remain constant (as it does not take part in loss or gain). 14: An atom is electrically neutral, on loss or gain of electrons why does it become charged?

Answer: An atom is electrically neutral because of same number of protons and electrons. But it becomes charged, to become stable atom, loses or gains electrons. Hence, Number of protons ≠ Number of electrons If it loses electrons p > e; hence +ve charge is obtained. If it gains electrons e > p; hence -ve charge is obtained. 15: What is valency? Explain different types of valencies. Answer: The combining capacity of an atom is called its valency. There are 2 types of valencies.

Some atoms also show zero valency when there outermost shell is completely filled. 16: With the help of an activity in daily life, how can you prove that atoms are divisible.

Answer: Activity

Take a scale, rub it on hair, try to attract a small bit of paper.
Now divide the bit of paper further into smaller pieces
Again bring the charged scale near to this pieces of papers.
You will observe that the bits of paper still get attracted.

Conclusion: This activity shows that atom contains charges and these charges are opposite in nature which shows the attraction. Hence here scale and paper both are oppositely charged and hence attract each other. Also, every atom has at least one sub-atomic particle.

Extra Questions for Class 9 Science Chapter 4 Structure of the Atom 8

17: In the structure of an atom why are protons present in the centre and are not pulled outside by the electrons as both are oppositely charged with same unit of charge?

Answer: Protons are heavy with mass 1 unit and hence are concentrated in the centre of the atom. The mass of electrons is negligible i.e.1/1800 times less than that of protons. Hence are not able to attract the protons and pull them out of the nucleus, although their charge is of same value.

18: According to you, among the structure of atom studied which model is correct and why?

Answer: Bohr’s model of an atom is the best model and is correct because it gives the explanation of nucleons (protons and neutrons) in the centre and how electrons revolve around the nucleons in their discrete, special orbits, so electrons don’t loose/radiate energy and remain bonded in their shell.

Long Answer Type Questions

1. Give an activity to understand the implications of Rutherford’s a scattering experiment by a gold foil.

Answer: To understand the implications of Rutherford’s a-particle scattering experiment: Activity: Let a child stand in front of a wall with his eyes closed. Let him throw stones at the wall from a distance. He will hear sound for each strike of stone on the wall. This is like a nucleus of the atom. But if a blind-folded child has to throw stones at a barbed-wire fence, most of the stones would not hit the fencing and no sound would be heard. This is because there are lots of gap in the fence which allows the stone to pass through them. This is like empty space in an atom through which a-particles will pass through. Based on the above activity and similar reasoning Rutherford concluded the a-particle scattering experiment as: (1) Most of the space inside the atom is empty as a-particles passed through the foil. (2) Very few particles deflected from their path, this show that positive charge occupies less space. (3) A very small fraction of a-particles are deflected by 180°, this shows that all the positive charge and mass of the gold atom were concentrated in a very small volume within the atom.

2: What are isotopes? State its characteristics, give uses of isotopes?

Answer: Atoms of same element with same atomic number but different mass number are isotopes. Characteristics: (1) Physical properties of the isotopes are different e.g. mass, density. (2) Chemical properties of the isotopes are same due to same number of electrons. Uses: (1) Uranium isotope is used as a fuel in nuclear reactor (U-235). (2) Cobalt isotope is used for treatment of cancer (Co-60). (3) Iodine isotope is used in the treatment of goitre.

3: Explain Rutherford’s α-particle scattering experiment and give its observation and conclusion drawn.

Answer: Rutherford’s α-particle scattering experiment: Fast moving α-particles were made to fall on a thin gold foil. Particles have + 2 charge and 4u mass, and considerable amount of energy.

Extra Questions for Class 9 Science Chapter 4 Structure of the Atom 9

Observations: (1) Most of the α-particles passed straight through the foil. (2) Some of the α-particles were deflected by small angles by the foil. (3) One out of every 12000 particles rebounded.

Conclusion from observation: (1) Most of the space inside the foil is empty. (2) Positive charge of atom occupies very less space. (3) Mass of the atom is concentrated in the centre with all positive charge concentrated in small volume within the atom.

4: Establish the relationship between atomic number, mass number, isotopes, isobars and valency of an atom.

Answer: Atomic number — Gives the number of protons (Z) Mass number — Gives the number of protons and neutrons (A) Isotopes — When atoms of same element have same number of protons (Z) but different number of a neutrons (s) such atoms are called isotopes. Isobars — When atom of different element have same mass number (A) but different atomic number (Z) such atoms are called isobars. Valency — It is the combining capacity of an atom.

Extra Questions for Class 9 Science Chapter 4 Structure of the Atom 10

Value Based Questions

1: Aryan could not solve the following question in the group; his group mate explained him and solved his difficulty. The question was as follows: What information do you get from the given figure about the atomic number, mass number and valency of the given atom X’. (a) What is the answer for-the above question? (b) Name the element X’. (c) What value of Aryan’s friend is reflected in this behaviour?

Extra Questions for Class 9 Science Chapter 4 Structure of the Atom 11

Answer: (a) The atomic number is 5. The mass number is 11. The valency is 3. (b) The element X’ is boron. (c) Aryan’s friend showed the value of helping and caring nature.

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NCERT Class 9 Science Chapter 4 Structure of the Atom Notes PDF Download

NCERT Class 9 Science Chapter 4 Structure of the Atom Notes have been largely compiled by teachers with near to 20 years of experience and after studying the last ten years of examination papers. Further, they are all designed with the latest academic year subject material so that any difference in the syllabus is accounted for as well. NCERT Class 9 Science Chapter 4 Structure of the Atom Notes are very useful and important because, it is necessary that all questions are answered in an efficient manner. By studying from these NCERT Science Chapter 4 Structure of the Atom Notes for class 12 and employing sample papers, students will no difficulty be able to alleviate any tension before exams as they will be fully prepared in advance for their board exams. Also, the NCERT Science Chapter 4 Structure of the Atom Notes for class 12 is easy to read and includes all the study material, all clearly described and in a concise manner. Students can also use the sample papers that SelfStudys provides for class 12 along with the NCERT Class 9 Science Chapter 4 Structure of the Atom Notes provided. Together, students will be prepared to answer every type of question like subjective and objective and aim for the best in their last year of school.

NCERT Class 9 Science Chapter 4 Structure of the Atom Notes PDF

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Class 9 Science Chapter 4 Notes Structure Of The Atom

NCERT Class 9 Science Chapter 4 Notes Structure Of The Atom on this step-by-step answer guide . In some of State Boards and CBSE schools, students are taught thru NCERT books. As the chapter comes to an end, students are requested few questions in an exercising to evaluate their knowledge of the chapter. Students regularly want guidance dealing with those NCERT Notes. It’s most effective natural to get stuck withinside the exercises while solving them so that you could assist students rating better marks, we have provided grade by grade NCERT answers for all exercises of Class 9 Science Structure Of The Atom so you can be searching for assist from them. Students have to solve those exercises carefully as questions withinside the very last exams are requested from those so these exercises at once have an impact on students’ final score. Find all NCERT Notes for Class nine Science Structure Of The Atom below and prepare for your tests easily.

Chapter 4 : Structure Of The Atom

A major challenge before the scientists at the end of the 19th century was to reveal the structure of the atom as well as to explain its important properties.

One of the first indications that atoms are not indivisible , comes from studying static electricity and the condition under which electricity is conducted by different substances.

Charged particles in matter

Many scientists contributed in revealing the presence of charged particles in an atom.

It was known by 1900 that the atom was not a simple , indivisible particle but contained at least one sub – atomic particle

The electron identified by J.J. Thomson.

Even before the electron was identified, E. Goldstein in 1886 discovered the presence of new radiations in a gas discharge and called them canal rays.

This sub-atomic particle had a charge, equal in magnitude but opposite in sign to that of the electron.

It was given the name of proton.

An electron is represented as ‘e – ‘ and a proton as ‘p + ‘.

The mass of a proton is taken as one unit and its charge as plus one.

The mass of an electron is considered to be negligible and its charge is minus one.

The Structure of an Atom

The discovery of two fundamental particles (electrons and protons) inside the atom, led to the failure of this aspect of Dalton’s atomic theory.

J.J. Thomson was the first one to propose a model for the structure of an atom.

THOMSON’S MODEL OF AN ATOM

Thomson proposed the model of an atom to be similar to that of a Christmas pudding.

The electrons , in a sphere of positive charge . were like currants ( dry fruits ) in a spherical Christmas pudding.

Thomson proposed that:

An atom consists of a positively charged sphere and the electrons are embedded in it.
The negative and positive charges are equal in magnitude. So , the atom as a whole is electrically neutral.

RUTHERFORD’S MODEL OF AN ATOM

Ernest Rutherford was interested in knowing how the electrons are arranged within an atom.

Rutherford designed an experiment for this.

In this experiment:

He selected a gold foil because he wanted as thin a layer as possible. This gold foil was about 1000 atoms thick.
α- particles are doubly – charged helium ions. Since they have a mass of 4 u, the fast – moving α – particles have a considerable amount of energy.
It was expected that α- particles would be deflected by the sub – atomic particles in the gold atoms. Since the α – particles were much heavier than the protons, he did not expect to see large deflections.

α – particle scattering experiment unexpected results

Most of the fast moving a particles passed straight through the gold foil.
Some of the a – particles were deflected by the foil by small angles.
Surprisingly one out of every 12000 particles appeared to rebound.

In the words of Rutherford, “This result was almost as incredible as if you fire a 15 – inch shell at a piece of tissue paper and it comes back and hits you”.

Rutherford concluded from the α – particle scattering experiment that

Most of the space inside the atom is empty because most of the α – particles passed through the gold foil without getting deflected.
Very few particles were delected from their path, indicating that the positive charge of the atom occupies very little space.
A very small fraction of α-particles were deflected by 180º, indicating that all the positive charge and mass of the gold atom were concentrated in a very small volume within the atom.

From the data he also calculated that the radius of the nucleus is about 10 5 times less than the radius of the atom.

Rutherford experiment of nuclear model of an atom, which had the following features:

There is a positively charged center in an atom called the nucleus.Nearly all the mass of an atom resides in the nucleus.
The electrons revolve around the nucleus in circular paths.
The size of the nucleus is very small as compared to the size of the atom.

Drawbacks of Rutherford’s model of the atom

The revolution of the electron in a circular orbit is not expected to be stable.
Any particle in a circular orbit would undergo acceleration.
During acceleration, charged particles would radiate energy.
The revolving electron would lose energy and finally fall into the nucleus.

If this were so, the atom should be highly unstable and hence matter would not exist in the form that. Atoms are quite stable.

BOHR’S MODEL OF ATOM

Neils Bohr put forward the following postulates about the model of an atom:

Only certain special orbits known as discrete orbits of electrons, are allowed inside the atom.
While revolving in discrete orbits the electrons do not radiate energy.

These orbits or shells are called energy levels, Energy levels.

These orbits or shells are represented by the letters K, L, M, N,… or the numbers, n = 1,2,3,4, ….

In 1932, J. Chadwick discovered another sub atomic particle which had no charge and a mass nearly equal to that of a proton.
Neutrons are present in the nucleus of all atoms , except hydrogenl.
A neutron is represented as ‘n’.
The sum of the masses of protons and neutrons present in the nucleus

How are Electrons Distributed in Different Orbits (Shells)?

The distribution of electrons into different orbits of an atom was suggested by Bohr and Bury.

Rules are followed for writing the number of electrons in different energy levels or shells:

The maximum number of electrons present in a shell is given by the formula 2n 2 . where ‘ n ‘ is the orbit.

first orbit or K – shell will be = 2 x 1 2 = 2.

second orbit or L – shell will be = 2 x 2 2 = 8.

third orbit or M – shell will be = 2 x 3 2 = 18.

fourth orbit or N – shell will be = 2 x 4 2 = 32 , and so on.

The maximum number of electrons that can be accommodated in the outermost orbit is 8.
Electrons are not accommodated in a given shell, unless the inner shells are filled.

Kossel and Lewis and Langmuir studied the electronic configuration of different elements.

It is observed that each element has a definite electronic configuration and normally, the electrons present in the outermost shell take part in chemical reactions of that element.

The outermost shell of an atom is known as the valence shell and the electrons present in the outermost shell are known as valence electrons.

Valence Electrons and Chemical Properties of the Elements

Chemical properties of the elements mainly depend on the number of valence electrons and not the total number of electrons present in an atom.

An element is chemically inert if it has 8 electrons in its outermost shell. Except helium , which has 2 electrons in its outermost shell , all other noble gases have 8 electrons ( octet ) in their valence shell and hence , all noble gases are highly unreactive and rather chemically inert.
Elements with 1 electron in their valence shell, for example, lithium (2, 1), sodium (2, 8, 1), etc, are very reactive
Elements with 7 electrons in their valence shell, for example, fluorine (2, 7), chlorine (2, 8, 7) etc, are also very reactive.
Elements having same number of valence electrons show similar chemical properties. For example, Li (2,1), Na (2, 8, 1) and K (2, 8, 8, 1) have one electron in their outermost shell. These elements show similar chemical properties. Similarly, fluorine, chlorine, bromine, etc., which are collectively called halogens, have similar chemical properties.
Elements having less than 4 electrons in their valence shell are normally metals and are reactive. Hydrogen and helium having 1 and 2 valence electrons respectively are exceptions.
Elements having 4, 5, 6 or 7 electrons in their outermost shell are normally nonmetals. For example, carbon nitrogen, oxygen and fluorine have 4, 5, 6 and 7 valence electrons respectively. These elements are chemically reactive.

Valency and Valence Electrons

Valency is defined as the number of valence electrons of an atom (element) which actually take part in the chemical combination or bond formation with other element.
The valency of an element is equal to the number of valence electrons if their number is 4 or less . For example, Na (2, 8, 1) has 1 valence electron and therefore, valency of sodium is 1. Similarly, carbon (2, 4) shows a valency of 4.

Electronic Concept of Valency

It is a well – known fact that noble gases like Helium ( He ) Neon ( Ne ) . Argon ( Ar ) . Krypton ( Kr ) and Xenon Xe are rather chemically inert . Except helium , which has 2 electrons in its valence shell , atoms of all noble gases have 8 electrons ( octet ) in their outermost shell or the valence shell This shows that the octet configuration is very stable
Octet Rule: Every system in nature tries to have the state of maximum stability. Therefore, reactive atoms (or elements) undergo chemical combination or bond formation in order to acquire octet configuration in their valence shell. This is called octet rule.

Types of Valency

The combining atoms of the elements try to acquire the nearest inert gas stable configuration mainly in two ways:
By loss or gain ( transfer ) of electrons between the combining atoms (electrovalency).
Atomic Number and Mass Number

ATOMIC NUMBER

It is the number of protons of an atom, It is denoted by Z.
All atoms of an element have the same atomic number, Z.
The atomic number is defined as the total number of protons present in the nucleus of an atom.

MASS NUMBER

Mass of an atom is practically due to protons and neutrons alone.
These are present in the nucleus of an atom.
Protons and neutrons are also called nucleons.
The mass of an atom resides in its nucleus.
For example, mass of carbon is 12 u because it has 6 protons and 6 neutrons, 6 u + 6 u = 12 u .

The mass number is defined as the sum of the total number of protons and neutrons present in the nucleus of an atom.

Isotopes are defined as the atoms of the same elements, having the same atomic number but different mass numbers.
Three isotopes of hydrogen atom, namely protium, deuterium and tritium.
The chemical properties of isotopes are similar but their physical properties are different.
If an element has no isotopes, then the mass of its atom would be the same as the sum of protons and neutrons in it.

Applications

An isotope of uranium is used as a fuel in nuclear reactors.
An isotope of cobalt is used in the treatment of cancer.
An isotope of iodine is used in the treatment of goitre.
Atoms of different elements with different atomic numbers.
which have the same mass number, are known as isobars.

Benefits of NCERT Class 9 Science Chapter 4 Notes Structure Of The Atom

NCERT Class 9 Science Chapter 4 Notes Structure Of The Atom contains extremely important points, and for each chapter, each concept has been simplified to make it easier to remember and increase your chances of achieving excellent exam results. Exam Preparation References Here are some tips on how these solutions can help you prepare for the exam.

This helps students solve many of the problems in each chapter and encourages them to make their concepts more meaningful.
NCERT Class 9 Science Chapter 4 Notes Structure Of The Atom encourage you to update your knowledge and refine your concepts so that you can get good results in the exam.
These notes are the best exam materials, allowing you to learn more about your week and your strengths. To get good results in the exam, it is important to overcome your weaknesses.
Most of the questions in the exam are formulated in a similar way to NCERT textbooks. Therefore, students should review the solutions in each chapter in order to better understand the topic.
It is free of cost.

Tips & Strategies for Class 9 Exam Preparation

Plan your course and syllabus and make time for revision
Please refer to the NCERT solution available on the cbsestudyguru website to clarify your concepts every time you prepare for the exam.
Use the cbsestudyguru learning app to start learning to successfully pass the exam. Provide complete teaching materials, including resolved and unresolved tasks.
It is important to clear all your doubts before the exam with your teachers or Alex (an Al study Bot).
When you read or study a chapter, write down algorithm formulas, theorems, etc., and review them quickly before the exam.
Practice an ample number of question papers to make your concepts stronger.
Take rest and a proper meal. Don’t stress too much.

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These Notes are designed by subject matter experts and provide solutions to every NCERT textbook questions.
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Ncert Solutions for Class 9 Science Chapter 4 Structure of atom

Chapter 4 Structure of the NCERT Solutions for Class 9 Science the Atom at INFINITY LEARN gives students answers to all of the questions in the NCERT Class 9 textbook , which follows the CBSE board’s guidelines. This article supplies students with study source material created by a team of specialists with extensive subject understanding. Students who solve NCERT Solutions for Class 9 Science will be able to achieve the highest possible score on the Class 9 CBSE Science Term II exam.

Our professionals at INFINITY LEARN employ language that is proficient and understandable to Class 9 students when preparing NCERT Solutions for Class 9 Science , supporting them in better comprehending the idea. This is founded on a concept-based strategy. These NCERT Solutions have been created with the CBSE’s preferred manner of answering in mind, and the allotment of marks in CBSE Term-II examinations has been taken into account to help students set out their answers correctly and therefore achieve the highest possible marks. The board’s NCERT textbook is created by a panel of experts who take into account the most recent developments in science and technology.

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NCERT Exemplar Solutions for Class 9 Science Chapter 4 are also offered.

Class 9 Science Chapter 4 CBSE Notes

NCERT Solutions for Class 9 Science Chapter 4 – Structure of The Atom

NCERT Solutions for Class 9 Science Chapter 4 – Structure of The Atom is categorized under Unit I – Matter – Its nature and behaviour, which fundamentally deals with the physical nature of matter and what makes up the particles that make up matter. The entire unit of matter is worth 23 points, with the Structure of the Atom chapter receiving 10 points. Students should practice utilizing the Science NCERT Solutions for Class 9 in order to achieve the highest possible grade.

This chapter is well-balanced. A thorough understanding of all of the concepts taught in this chapter can help you earn up to ten points just from this chapter. From this chapter, about 2 questions with 5 marks each appear in the CBSE Term II examination and are projected to appear again the following year.

Subtopics addressed in Chapter 4 of Class 9 Science: Structure of The Atom:

Students can use the NCERT Solutions for Class 9 Science Chapter 4 to make quick references to help them understand the above and other difficult concepts. Furthermore, these answers are available as a downloaded PDF that can be examined both online and offline.

Class 9 Science Chapter 4 Number 4 Exercises List 1

Number 4.1 – Charged particles in matter 2 Question (2 short)
Number 4.2 – The structure of an atom 4 Question (4 short)
Number 4.2.4 – Neutrons 2 Question (2 short)

Number 4.3 – How are electrons distributed

indifferent orbits(shells)? 2 Question (1 long, 1 short)

Number 4.4 – Valency 1 Question (1 long)

Number 4.5 – Atomic number and mass number 2 Question (2 long)
Number 4.6 – Isotopes 2 Question (1 long, 1 short)
Exercise Solutions – 19 Question (6 long, 9 short, 4 MCQ)

Chapter 4 – Structure of the Atom NCERT Solutions for Class 9 Science

In this chapter, we learn about J.J. Thomson’s and Goldstein’s contributions to the discovery of electrons and protons, respectively. Electrons are implanted in the positive sphere, according to J.J. Thomson’s idea. Rutherford’s alpha-particle scattering experiment paved the way for the discovery of the atomic nucleus. We also discover how successful Neil Bohr’s model was in explaining how electrons are scattered in various orbits around the nucleus.

This chapter also discusses J. Chadwick’s proposal for the discovery of neutrons in an atom, leading to the conclusion that there are three subatomic particles: protons, neutrons, and electrons. It also clarifies terms like valency, atomic number, and mass number, which are crucial for identifying elements and their behavioural characteristics. Access the NCERT Solutions for Class 9 of this chapter of science to learn more about these ideas.

Overall, it aids us in understanding what distinguishes an atom from atoms of other elements, the concept of atom indivisibility, the representation of elements through mass number and atomic mass, and the basic constituents of an atom.

NCERT Solutions for Class 9 Science Chapter 4 – Structure of the Atom: Main Characteristics

NCERT Solutions make it possible for pupils to relax while studying for the CBSE Class 9 Term II examination.
While solving, calculations and electronic configurations were thoroughly described.
Wherever possible, diagrams have been included to aid visual learning.
Numerical problems regarding determining the valency of elements have been thoroughly investigated.
Tables are used in comparison questions to aid learning and comprehension.
In order to remember at a glance, pointers were employed in the solutions.

NCERT Solutions for Class 9 Science Chapter 4 Frequently Asked Questions

List the topics and subtopics enclosed in NCERT Solutions for Class 9 Science, Chapter 4.

Chapter 4 of NCERT Solutions for Class 9 Science covers the following themes and subtopics:

4.1 Charged particles in matter

4.2 The structure of an atom

4.2.1 Thomson’s model of an atom

4.2.2 Rutherford’s model of an atom

4.2.3 Bohr’s model of an atom

4.2.4 Neutrons

4.3 How are electrons distributed in different orbits(shells)?

4.4 Valency

4.5 Atomic number and mass number

4.5.1 Atomic number

4.5.2 Mass number

4.6 Isotopes

4.6.1 Isobars

In Chapter 4 of NCERT Solutions for Class 9 Science, how many exercises are there?

The exercises existing in Chapter 4 of NCERT Solutions for Class 9 Science are –

Number 4.1 – Charged particles in matter 2 Questions (2 short)

Number 4.2 – The structure of an atom 4 Questions (4 short)

Number 4.2.4 – Neutrons 2 Questions (2 short)

Indifferent orbits(shells) – 2 Questions (1 long, 1 short)

Number 4.5 – Atomic number and mass number 2 Questions (2 long)

Number 4.6 – Isotopes 2 Questions (1 long, 1 short)

Exercise Solutions – 19 Questions (6 long, 9 short, 4 MCQ)

How can I get the NCERT Solutions for Science Fourth chapter for the 9th class online?

INFINITY LEARN has NCERT Solutions for Class 9 Science Chapter 4 available. These solutions have been produced by specialists to assist students with their CBSE Term II test preparation. The solutions include clear explanations in easy-to-understand language to help students gain a better understanding of the concepts. Students can save a lot of time by using the solutions PDF to get the proper answer to each question.

Class 9 Civics Case Study Questions Chapter 4 Working of Institutions

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Case study Questions on Class 9 Social Science Chapter 4 are very important to solve for your exam. Class 9 Social Science Chapter 10 Case Study Questions have been prepared for the latest exam pattern. You can check your knowledge by solving case study-based questions for Class 9 Civics Case Study Questions Chapter 4 Working of Institutions

Join our Telegram Channel, there you will get various e-books for CBSE 2024 Boards exams for Class 9th, 10th, 11th, and 12th.

In CBSE Class 9 Social Science Paper, Students will have to answer some questions based on Assertion and Reason. There will be a few questions based on case studies and passage-based as well. In that, a paragraph will be given, and then the MCQ questions based on it will be asked.

Working of Institutions Case Study Questions With Answers

Here, we have provided case-based/passage-based questions for Class 9 Social Science Chapter 4 Working of Institutions

Case Study 1: The government is responsible for ensuring security to the citizens and providing facilities for education and health to all. It collects taxes and spends the money thus raised on administration, defense, and development programs. It formulates and implements several welfare schemes. Some people have to make decisions on how to go about these activities. Others have to implement these decisions. If disputes arise on these decisions or in their implementation, there should be someone to determine what is right. and what is wrong. It is important that everyone should know who is responsible for doing what. It is also important that these activities keep taking place even if the persons in key positions change. So, to attend to all these tasks, several arrangements are made in all modern democracies. Such arrangements are called institutions. Democracy works well when these institutions perform functions assigned to them. The Constitution of any country lays down basic rules on the powers and functions of each institution. We see several such institutions at work. The Prime Minister and the Cabinet are institutions that take all important policy decisions. The Civil Servants, working together, are responsible for taking steps to implement the ministers’ decisions. Supreme Court is an institution where disputes between citizens and the government are finally settled.

What are the main activities of a government? (a) Responsibility for ensuring security to the citizens (b) Providing education and health facilities (c) Implementing several welfare schemes (d) All of the above

Answer: (d) All of the above

If disputes arise regarding the activities of the government, identify the correct option. I. The Supreme Court should be consulted. II. Parliament will take the decision. III. The Prime Minister will take the decision. Codes (a) Only I (b) Both I and II (c) Only III (d) All to these

Answer: (a) Only I

Which of the following is/are regarded as institutions in democracy? (a) The Prime Minister and the Cabinet (b) The Civil Servants (c) The Supreme Court (d) All of these

Which of the following is considered as reason for delay in the decision making procedure of democracy? (a) Working with institutions is not easy. (b) Rules and regulations of institutions bind the hands of leaders. (c) It involves meetings, committees and routines. (d) All of the above

Which of the following can be regarded as better option instead of institutions in democracy? (a) One person takes all decisions without any rules, procedures and meeting. (b) A group of people take all decisions. (c) Judiciary can take all decisions. (d) None of the above

Answer: (d) None of the above

Which of the following is/are correct regarding the institutions in democracy? (a) Institutions make it difficult to have a good decision taken very quickly. (b) Institutions make it equally difficult rush through a bad decision. (c) Both (a) and (b) (d) None of these

Case Study 2: In a democracy, institutions play a crucial role in ensuring the smooth functioning of the government and the protection of citizens’ rights. The three main institutions in India’s democratic setup are the Legislature, the Executive, and the Judiciary. The Legislature consists of elected representatives who make laws and debate issues in the Parliament and State Legislative Assemblies. The Executive comprises the President, the Prime Minister, and the Council of Ministers, who are responsible for implementing laws and policies. The Judiciary, headed by the Supreme Court, is responsible for interpreting and upholding the Constitution, resolving disputes, and safeguarding the rights of citizens. These institutions work independently of each other but maintain a system of checks and balances to prevent the abuse of power. The working of these institutions is essential for the proper functioning of democracy and the protection of the rights and interests of the people.

What are the three main institutions in India’s democratic setup? a) Judiciary, Parliament, and Council of Ministers b) Legislature, Executive, and Judiciary c) President, Prime Minister, and Cabinet d) Rajya Sabha, Lok Sabha, and State Legislative Assemblies

Answer: b) Legislature, Executive, and Judiciary

What is the role of the Legislature in a democracy? a) Implementing laws and policies b) Interpreting and upholding the Constitution c) Making laws and debating issues d) Resolving disputes and safeguarding citizens’ rights

Answer: c) Making laws and debating issues

Who is responsible for implementing laws and policies in India? a) President, Prime Minister, and Council of Ministers b) Supreme Court and its judges c) Members of Parliament and State Legislative Assemblies d) Election Commission of India

Answer: a) President, Prime Minister, and Council of Ministers

Which institution is responsible for interpreting and upholding the Constitution? a) Parliament b) President c) Supreme Court d) Election Commission of India

Answer: c) Supreme Court

How do the institutions of democracy maintain a system of checks and balances? a) By implementing laws and policies b) By interpreting and upholding the Constitution c) By making laws and debating issues d) By working independently but overseeing each other’s actions

Answer: d) By working independently but overseeing each other’s actions

Hope the information shed above regarding Case Study and Passage Based Questions for Class 9 Social Science Chapter 4 Working of Institutions with Answers Pdf free download has been useful to an extent. If you have any other queries about CBSE Class 9 Social Science Working of Institutions Case Study and Passage Based Questions with Answers, feel free to comment below so that we can revert back to us at the earliest possible By Team Study Rate

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Case Study Questions Class 9 Science Work and Energy

Case study questions class 9 science chapter 11 work and energy.

CBSE Class 9 Case Study Questions Science Work and Energy. Important Case Study Questions for Class 9 Exam. Here we have arranged some Important Case Base Questions for students who are searching for Paragraph Based Questions Work and Energy.

At Case Study Questions there will given a Paragraph. In where some Questions will made on that respective Case Based Study. There will various types of marks will given 1 marks, 2 marks, 3 marks or 4 marks.

CBSE Case Study Questions Class 9 Science – Work and Energy

(1 ) Work done by force acting on an object is equal to the magnitude of the force multiplied by the distance moved in the direction of the force. Work has only magnitude and no direction. Work done is negative when the force acts opposite to the direction of displacement. Work done is positive when the force is in the direction of displacement.The unit of work is newton-metre (N m)or joule (J).

(i) Work done is

(a) Scalar quantity

(b) Vector quantity

(d) None of these

(ii) When force acts against the direction of displacement then work done will be

(a) positive

(b) negative

(iii) SI unit of work is

(a) Joule(J)

(b) Newton meter(N-m)

(iv)You are lifting stone from floor. Work is done by theforce exerted by you on the stone. Theobject moves upwards. The force youexerted is in the direction ofdisplacement. However, there is theforce of gravity acting on the object. Which one of these forces is doingpositive work?

Which one is doing negative work?

(v) Define 1J of work.

Answer key-1

(iv) Here work done by you is positive work as work is being done in the direction of displacement unlike in case of gravitational force which acts in downward direction against the direction of displacement which is in upward direction.

(v) When 1 Newton of force acts on body and body displaces from its position by 1 meter then the work done is said to be 1 joule (J).

(2) A moving object can do work. An object moving faster can do more work than an identical object moving relatively slow. A moving bullet, blowing wind, a rotating wheel, a speeding stone can do work. How does a bullet pierce the target? How does the wind move the blades of a windmill? Objects in motion possess energy. We call this energy kinetic energy.

Thus, the kinetic energy possessed by an object of mass, m and moving with a uniform velocity, v is

KE = ½ *mv 2

The energy possessed by an object is thus measured in terms of its capacity of doing work. The unit of energy is, therefore, the same as that of work, that is, joule (J).

(i) Energy possessed by body which is in motion is called

(a) Potential energy

(b) Kinetic energy

(ii) Which of the following has same unit?

(a) Potential energy and Force

(b) Kinetic energy and work

(iii) Kinetic energy depends

(a) Inversely on velocity of body

(b) Directly on square of velocity of body

(iv) Define kinetic energy of body. Give its SI unit

(v) Is kinetic energy scalar or vector? Justify your answer

Answer key-2

(iv) Energy possessed by object due to its motion is called as kinetic energy. Its SI unit is N-m or Joule(J).

(v) kinetic energy is scalar quantity as it is a work done and work done is scalar quantity hence kinetic energy is also scalar quantity and doesn’t have any direction.

(3) Lift an object through a certain height. The object can now do work. It begins to fall when released. This implies that it has acquired some energy. If raised to a greater height it can do more work and hence possesses more energy. From where did it get the energy? In the above situations, the energy gets stored due to the work done on the object. The energy transferred to an object is storedas potential energy if it is not used to cause a change in the velocity or speed of the object.An object increases its energy when raisedthrough a height. This is because work isdone on it against gravity while it is being raised. The energy present in such an objectis the gravitational potential energy.The gravitational potential energy of anobject at a point above the ground is definedas the work done in raising it from the ground by height h

to that point against gravity.Let the work done on the object against gravity beW. That is,

work done, W = force × displacement

Therefore potential energy (PE)= mg*h.

(i) Energy possessed by body due to its position is called

(ii) SI unit of potential energy is

(iii)You do work while winding the key of a toy car. The energy transferred to the spring inside is stored as

(iv)Find the energy possessed by an object of mass 5kg when it is at a height of 10 m above the ground. Given, g = 9.8 m/s 2 .

(v)Find the work done by Gravity on an object of mass 5 kg which moves from height 10m to ground when it is released from height of 10 m. Given, g = 9.8 m/s 2 .

Answer key-3

(iv) we have potential energy as

=5 ×9.8 ×10

(v) work done, W = force × displacement

= 5 ×9.8 ×10

(4) The form of energy can be changed from one form to another. What happens to the totalenergy of a system during or after the process?Whenever energy gets transformed, the totalenergy remains unchanged. This is the law ofconservation of energy. According to this law, energy can only be converted from one form to another it can neither be created nor destroyed. The total energy before and after the transformation remains the same.The lawof conservation of energy is valid inall situations and for all kinds of transformations. Thus during motion the sum of the potential energy and kinetic energy of the object would be the same at all points. That is, potential energy + kinetic energy = constant.Andcalled as mechanical energy.

(i) Which of the energy conversion occur in electric iron?

(a) Electric energy converted into heat energy

(b) Electric energy converted into light energy

(ii) When ball drops from height which of the energy conversion takes place

(a) Gravitational potential energy converted into kinetic energy

(b) Kinetic energy converted into Gravitational potential energy

(iii) When ball is thrown vertically upward which of the following quantity remains constant?

(iv) State law of conservation of energy.

(v) In hydroelectric power plant which energy conversion happens?

Answer key-4

(iv) This is the law ofconservation of energy. According to this law,energy can only be converted from one form to another it can neither be created nor destroyed. The total energy before and after the transformation remains the same.

(v) In hydroelectric power plant potential energy of water reservoir is converted into electric energy.

(5 ) A more powerful vehiclewould complete a journey in a shorter timethan a less powerful one. We talk of the powerof machines like motorbikes and motorcars.The speed with which these vehicles changeenergy or do work is a basis for theirclassification. Power measures the speed ofwork done, that is, how fast or slow work isdone. Power is defined as the rate of doingwork or the rate of transfer of energy. If anagent does a work W in time t, then power isgiven by

P= work/time

P= W/T. The unit of power is watt.

(i) The rate of doing work is defined as

(ii) Total energy consumed divided by total time taken is called as

(a) Average power

(b) Instantaneous power

(iii) Let A and B having same weight start climbing the rope and reach height of 10m. Let A takes 10sec while B takes 12sec then work done

(a) By both will be same

(b) By A is more than work done by B

(iv) Define 1 Watt of power

(v) An electric bulb of 20W is used for 5h per day. Calculate the ‘units’ of energy consumed in one day by the bulb.

Answer key-5

(iv) A power is said to be 1 watt when 1 joule of work is done within 1 second of time.

(v) Power of electric bulb = 20 W

Time used, t = 5 h

Energy = power × time taken

= 0.02kW × 5 h

= 0.10 kW h

= 0.10‘units’.

The energy consumed by the bulb 0.10 units

Jaru mitaya

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CBSE Notes For Class 9
Class 9 Science Notes
Chapter 4: Structure Of The Atom

Structure Of The Atom Class 9 CBSE Notes - Chapter 4

Essentially, the structure of an atom comprises protons, neutrons and electrons. These basic components provide the mass and charge of the atoms. The nucleus comprises protons and neutrons, with the electron orbiting around that.

Introduction to the Structure of an Atom

Atoms are the building blocks of matter. It is the smallest unit of matter that is composed of three sub-atomic particles: the proton, the neutron and the electron.

To know more about Atomic Structure, visit here .

Cathode Ray Experiment

J. J. Thomson discovered the existence of electrons.
He did this using a cathode ray tube, which is a vacuum-sealed tube with a cathode and anode on one end that created a beam of electrons travelling towards the other end of the tube.
The air inside the chamber is subjected to high voltage, and electricity flows through the air from the negative electrode to the positive electrode.
The characteristics of cathode rays (electrons) do not depend upon the material of electrodes and the nature of the gas present in the cathode ray tube.
The experiment showed that the atom was not a simple, indivisible particle and contained at least one subatomic particle – the electron.

To know more about Cathode Ray Experiment, visit here .

Electrons are the negatively charged sub-atomic particles of an atom.
The mass of an electron is considered to be negligible, and its charge is -1.
The symbol for an electron is e –
Electrons are extremely small.
They are found outside the nucleus.

Thomson’s Model of an Atom

According to Thomson,(i) An atom consists of a positively charged sphere and the electrons are embedded in it. (ii) The negative and positive charges are equal in magnitude. So, the atom as a whole is electrically neutral
The first model of an atom to be put forward and taken into consideration.
He proposed a model of the atom be similar to that of a Christmas pudding/watermelon.
The red edible part of the watermelon is compared with the positive charge in the atom.
The black seeds in the watermelon are compared with the electrons which are embedded on it.

To know more about Thomson’s Model, visit here .

Radioactivity

Radioactivity is the term for the process by which an unstable nucleus of an atom loses energy by giving out particles.
It does so by giving out particles such as alpha and beta particles.
This process is spontaneous.
An atom is unstable if the nucleus has an imbalance, meaning a difference in the protons and neutrons.

To know more about Radioactivity, visit here .

Rutherford Model

Rutherford’s experiment and observations.

In this experiment, fast-moving alpha (α)-particles were made to fall on a thin gold foil. His observations were:

A major fraction of the α-particles bombarded towards the gold sheet passed through it without any deflection, and hence most of the space in an atom is empty .
Some of the α-particles were deflected by the gold sheet by very small angles, and hence the positive charge in an atom is not uniformly distributed .
The positive charge in an atom is concentrated in a very small volume .
Very few of the α-particles were deflected back; that is, only a few α-particles had nearly 180o angle of deflection. So the volume occupied by the positively charged particles in an atom is very small as compared to the total volume of an atom .

For more information on The Gold Foil Experiment, watch the below video

Rutherford’s Model of an Atom

Rutherford concluded the model of the atom from the α-particle scattering experiment as follows:

(i) There is a positively charged centre in an atom called the nucleus. Nearly all the mass of an atom resides in the nucleus.

(ii) The electrons revolve around the nucleus in well-defined orbits.

(iii) The size of the nucleus is very small compared to the size of the atom.

Drawbacks of Rutherford’s Model

He explained that the electrons in an atom revolve around the nucleus in well-defined orbits. Particles in a circular orbit would experience acceleration.
Thus, the revolving electron would lose energy and finally fall into the nucleus.
But this cannot take place as the atom would be unstable, and the matter would not exist in the form we know.

Be More Curious!!!

The Millikan’s Oil Drop Experiment was an experiment performed by Robert A. Millikan and Harvey Fletcher in 1909 to measure the charge of an electron.
In the experiment, Millikan allowed charged tiny oil droplets to pass through a hole into an electric field.
By varying the strength of the electric field, the charge over an oil droplet was calculated, which always came as an integral value of ‘e.’
The conclusion of this is that the charge is said to be quantized, i.e. the charge on any particle will always be an integral multiple of e which is 1.6*10 -19

To know more about Rutherford Model, visit here .

Neil Bohr Model

Properties of electrons, protons and neutrons.

Bohr’s Model of an Atom

Bohr came up with the following postulates to overcome the objections raised against Rutherford’s model.

Electrons revolve around the nucleus in stable orbits without the emission of radiant energy. Each orbit has a definite energy and is called an energy shell or energy level.
An orbit or energy level is designated as K, L, M, and N shells. When the electron is in the lowest energy level, it is said to be in the ground state.
An electron emits or absorbs energy when it jumps from one orbit or energy level to another.
When it jumps from a higher energy level to a lower energy level, it emits energy, while it absorbs energy when it jumps from a lower energy level to a higher energy level.

To know more about Bohr Model, visit here .

Orbits are energy shells surrounding the nucleus in which electrons revolve.

Electron Distribution in Different Orbits

The distribution was suggested by Bohr and Bury.

The maximum number of electrons present in a shell is given by the formula 2n 2 , where ‘n’ is the orbit number or energy level index, 1,2,3,….
The maximum number of electrons in different shells are as follows: the first orbit will have 2*1 2 =2, the second orbit will have 2*2Msup>2=8, the third orbit will have 2*3 2 =18, the fourth orbit 2*4 2 =32 and so on.
The shells are always filled in a step-wise manner from the lower to higher energy levels. Electrons are not filled in the next shell unless previous shells are filled.
The electrons present in the outermost shell of an atom are known as the valence electrons.
The combining capacity of the atoms or their tendency to react and form molecules with atoms of the same or different elements is known as the valency of the atom.
Atoms of elements, having a completely filled outermost shell, show little chemical activity.
Their combining capacity or valency is zero.
For example, we know that the number of electrons in the outermost shell of hydrogen is 1, and in magnesium, it is 2.
Therefore, the valency of hydrogen is 1 as it can easily lose 1 electron and become stable.
On the other hand, that of magnesium is 2 as it can lose 2 electrons easily and also attain stability.

To know more about Valency, visit here .

Atomic Number

The number of protons found in the nucleus of an atom is termed the atomic number. It is denoted by the letter ‘Z’.

Mass Number and Representation of an Atom

To know more about Atomic Number and Mass number, visit here .

Isotopes and Isobars

To know more about Isotopes and Isobars, visit here .

Calculation of Mass Number for Isotopic Elements

When an element has an isotope, the mass number can be calculated by the different proportions it exists in.

This does not mean that any Carbon atoms exist with a mass number of 12.02u. If you take a certain amount of Carbon, it will contain both isotopes of Carbon, and the average mass is 12.02 u.

To discover more questions or relevant concepts on Structure Of Atom Class 9 Notes, register at BYJU’S.

Frequently Asked Questions on CBSE Class 9 Geography Notes Chapter 4: Structure of an Atom

What are the features of ‘thomas’ atomic model’.

J.J. Thomson’s experiments with cathode ray tubes showed that all atoms contain tiny negatively charged subatomic particles or electrons. Thomson proposed the plum pudding model of the atom.

Who was ‘Ernest Rutherford’?

Ernest Rutherford was a New Zealand physicist who came to be known as the father of nuclear physics.

What did ‘Neils Bohr’ discover?

Niels Bohr proposed a theory for the hydrogen atom, based on quantum theory, that some physical quantities only take discrete values.

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Class 9 Science Case Study Questions Chapter 4 Structure of Atom
Case study Questions on Class 9 Science Chapter 4 are very important to solve for your exam. Class 9 Science Chapter 4 Class 9 Science Case Study Questions have been prepared for the latest exam pattern. You can check your knowledge by solving case study-based questions for Class 9 Science Chapter 4 Structure of Atom
Case Study Questions Class 9 Science
Statement 1 - Positively charged centre in an atom called the nucleus. Statement 2 - The electrons revolve around the nucleus in circular paths. Statement 3 - Nearly all the mass of an atom resides in the nucleus. Statement 4 - The size of the nucleus is very small as compared to the size of the atom. (a) Only 2.
Case Study and Passage Based Questions for Class 9 Science Chapter 4
Case Study Questions for Class 9 Science Chapter 4 Structure of Atom In CBSE Class 9 Science Paper, Students will have to answer some questions based on Assertion and Reason. There will be a few questions based on case studies and passage based as well. In that, a paragraph will be given, and then questions based on it … Continue reading Case Study and Passage Based Questions for Class 9 ...
Class 9 Science Case Study Questions PDF Download
This article aims to present a comprehensive collection of case study questions for Class 9 Science, covering various topics and concepts. Join our Telegram Channel, there you will get various e-books for CBSE 2024 Boards exams for Class 9th, 10th, 11th, and 12th. CBSE Class 9 Science Exam will have a set of questions based on case studies in ...
Class 9 Science Case Study Questions
Case study questions in Class 9 Science. The inclusion of case study questions in Class 9 science CBSE is a great way to engage students in critical thinking and problem-solving. By working through real-world scenarios, Class 9 Science students will be better prepared to tackle challenges they may face in their future studies and careers.
Case Study Questions of Chapter 4 Structure of Atom PDF Download
Class 9 Science Chapter 4 Case Study Questions have been prepared for the latest exam pattern. You can check your knowledge by solving case study-based questions for Class 9 Science Chapter 4 Structure of Atom. In CBSE Class 9 Science Paper, Students will have to answer some questions based on Assertion and Reason. There will be a few questions ...
NCERT Solutions for Class 9 Science Chapter 4 Structure of ...
Answer: (i) The atomic number is equal to the number of protons. Therefore, the atomic number of the atom is 8. (ii) Since the number of both electrons and protons is equal, therefore, the charge on the atom is 0. Question 2: With the help of Table 4.1, find out the mass number of oxygen and sulphur atom.
NCERT Solutions for Class 9 Science Chapter 4 Structure of the Atom
The exercises in Chapter 4 of NCERT Solutions for Class 9 Science are. Number 4.1 - Charged particles in matter 2 Questions ( 2 short) Number 4.2 - The structure of an atom 4 Questions ( 4 short) Number 4.2.4 - Neutrons 2 Questions ( 2 short) Number 4.3 - How are electrons distributed.
NCERT Solutions for Class 9 Science Chapter 4
Download NCERT Solutions for Class 9 Science Chapter 4 - free PDF. Class 9 Science Chapter 4 describes the structure of the atom. In this chapter, students will discover novel ideas and hypotheses that have been developed and validated by several scientists. Applying the newly taught ideas would be much simpler if you use the Vedantu-prepared ...
NCERT Solutions for Class 9 Science Chapter 4 Structure of the Atom
on October 18, 2023, 5:34 AM. NCERT Solutions for Class 9 Science Chapter 4 Structure of the Atom in Hindi and English Medium prepared for new session 2024-25. Class 9 Science chapter 4 is modified and revised as per the new rationalised NCERT textbooks issued for academic year 2024-25.
NCERT Solutions for Class 9 Science Chapter 4 Structure of the Atom
23rd December 2023. NCERT Solutions for Class 9 Science (Chemistry) Chapter 4 Structure of the Atom provides detailed answers for all in-text and exercise Questions. These solutions contain an in-depth explanation of each topic involved in the chapter. All these solutions are prepared by expert teachers and updated for the current academic session.
NCERT Solutions for Class 9 Science Chapter 4 Structure of the Atom
Answer. (i) The atomic number is equal to the number of protons. Therefore, the atomic number of the atom is 8. (ii) Since the number of both electrons and protons is equal, therefore, the charge on the atom is 0. 2. With the help of Table 4.1, find out the mass number of oxygen and sulphur atom. Answer.
NCERT Solutions for Class 9 Science Chapter 4 Structure of Atom
Answer: (i) Atomic number: The atomic number of an element is equal to the number of protons in the nucleus of its atom. e.g., Oxygen has 6 protons hence atomic no. = 6. (ii) Mass number: The mass number of an atom is equal to the number of protons and neutrons in its nucleus.
Extra Questions for Class 9 Science Chapter 4 Structure of ...
The mass number is 11. The valency is 3. (b) The element X' is boron. (c) Aryan's friend showed the value of helping and caring nature. Extra questions for Class 9 Science Chapter 4 Structure of the Atom with answers is given below. Our subject expert prepared these solutions as per the latest.
NCERT Class 9 Science Chapter 4 Structure of the Atom ...
Students who practice these Science Chapter 4 Structure of the Atom notes will find that every concept is described in a lucid manner including the formulas, equations, diagrams and important questions. These NCERT Science Chapter 4 Structure of the Atom Notes for Class 9 can further be used to conduct quick revisions before examinations.
Case Study Questions Class 9 Science Matter in our Surroundings
At Case Study Questions there will given a Paragraph. In where some Questions will made on that respective Case Based Study. There will various types of marks will given 1 marks, 2 marks, 3 marks or 4 marks. CBSE Case Study Questions Class 9 Science - Matter in our Surroundings Case Study 1: 1.) A matter is anything that has mass and occupies ...
NCERT Exemplar Class 9 Science Solutions for Chapter 4
NCERT Exemplar Solutions for Class 9 Science Chapter 4 Structure of Atom help students to learn the concepts thoroughly discussed in CBSE Class 9 Structure of Atom. Referring to NCERT Exemplar aids in laying a strong foundation for students' future studies. Topics involved here are the basics and are helpful throughout their life.
Class 9 Science Chapter 4 Notes Structure Of The Atom
NCERT Class 9 Science Chapter 4 Notes Structure Of The Atom on this step-by-step answer guide . In some of State Boards and CBSE schools, students are taught thru NCERT books. As the chapter comes to an end, students are requested few questions in an exercising to evaluate their knowledge of the chapter. Students regularly want guidance dealing ...
Ncert Solutions for Class 9 Science Chapter 4 Structure of atom
The exercises existing in Chapter 4 of NCERT Solutions for Class 9 Science are -. Number 4.1 - Charged particles in matter 2 Questions (2 short) Number 4.2 - The structure of an atom 4 Questions (4 short) Number 4.2.4 - Neutrons 2 Questions (2 short) Number 4.3 - How are electrons distributed.
Class 9 Civics Case Study Questions Chapter 4 Working of Institutions
Here, we have provided case-based/passage-based questions for Class 9 Social Science Chapter 4 Working of Institutions. Case Study 1: The government is responsible for ensuring security to the citizens and providing facilities for education and health to all. It collects taxes and spends the money thus raised on administration, defense, and ...
Case Study Questions Class 9 Science
CBSE Case Study Questions Class 9 Science - Work and Energy. (1) Work done by force acting on an object is equal to the magnitude of the force multiplied by the distance moved in the direction of the force. Work has only magnitude and no direction. Work done is negative when the force acts opposite to the direction of displacement.
Structure Of The Atom Class 9 Notes
Structure Of The Atom Class 9 CBSE Notes - Chapter 4. Essentially, the structure of an atom comprises protons, neutrons and electrons. These basic components provide the mass and charge of the atoms. The nucleus comprises protons and neutrons, with the electron orbiting around that.
Case Study and Passage Based Questions for Class 9 Science Chapter 9
Last modified on:2 years agoReading Time:4MinutesCase Study Questions for Class 9 Science Chapter 4 Structure of Atom In CBSE Class 9 Science Paper, Students will have to answer some questions based on Assertion and Reason. There will be a few questions based on case studies and passage based as well. In that, a paragraph will be given, and then…

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Extra Questions on 9th Science Chapter 4

Nucleus of an atom has positive charge on it. Establish.

Were neutrons known at the time Rutherford performed the scattering experiment?

Why are isotopes of an element chemically similar?

Why do elements which exist as isotopes have fractional atomic masses?

Why is a proton not a universal particle like electron?

Important Questions on 9th Science Chapter 4

What are the limitations of Rutherford’s model of the atom?

Define valency by taking examples of silicon and oxygen.

Explain Atomic number with examples.

What do you understand by isobars?

If Z = 3, what would be the valency of the element? Also, name the element.

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NCERT Solutions for Class 9 Science Chapter 4 Structure of the Atom

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Structure Of The Atom Class 9 CBSE Notes - Chapter 4

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