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

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NCERT Chapter 4 Structure of the Atom Class 9 Questions and Answers: FREE PDF Download

The updated NCERT Solutions for Chapter 4 structure of the atom class 9 is now available on Vedantu. Students can download the FREE PDF and refer to these solutions from our website to solve the structure of the atom class 9 questions and answers easily.

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Table of Content
1. NCERT Chapter 4 Structure of the Atom Class 9 Questions and Answers: FREE PDF Download
2. Glance on NCERT Solutions for Structure of The Atom Class 9
3. Access NCERT Solutions for Class 9 Chapter 4 Science - Structure of the Atom
4. Topics Covered in Class 9 Chapter 4 Science
5. Benefits of NCERT Solutions for Class 9 Science Chapter 4 Structure of the  Atom
6. Important Study Material Links for Class 9 Chapter 4 Science
7. Conclusion
8. NCERT Solutions for Class 9 Science - Other Chapter-Wise Links 
9. Important Study Material Links for Class 9 Science
FAQs


All the topics and sub-topics, such as charged particles, structure of the atom, Thomson’s model, Rutherford model, Bohr’s model, valency, etc., covered in Class 9 Science chapter 7 have been included in these solutions according to the latest Class 9 NCERT Science syllabus. Therefore, students can rely upon these NCERT Solutions to prepare for their exams.


Glance on NCERT Solutions for Structure of The Atom Class 9

  • You can opt for atomic structure class 9 NCERT Solutions for Science for Upcoming Exams, and you can find the solutions for all the science chapters below.

  • Class 9 science chapter 4 question answers you will also explore the 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 stabilises 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 class 9 science chapter 4 question answers PDF available here to find the right answers to all the questions.

  • Class 9 Science Ch 4 can help students analyse their level of preparation and understanding of concepts.

  • 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, structure of the atom class 9 PDF, and judge your understanding of the concepts. 

  • You can also use NCERT Solutions atomic structure class 9 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.

  • Class 9 chapter 4 science topics are included according to the revised academic year 2024-25 syllabus.

  • Cass 9 structure of atom question answers provides resources such as class notes, important concepts, and formulas exemplar solutions.

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

Ans:

Sketch of Bohr’s model


6. Name the three subatomic particles of an atom.

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

i. Proton

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 $2,4$


Distribution of electron in carbon


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

The distribution of electrons in sodium atom is given by: 

First orbit or K-shell = $2$ electrons 

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 \[2,\text{ }8,1\].


Distribution of electron in sodium atom


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?

Ans: 

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.

  1. 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.

  1. In case of sulphur, 

The valency of sulphur = 8 − 6 = 2

  1. 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?

Ans: 

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.

Ans:

Symbol

Electron

Proton

Neutron

H

1

1

0

D

1

1

1

T

1

1

2


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

Ans:

Two isotopes of carbon are  :

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

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

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  :

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

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

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:

Electron

Proton

Neutron

1. It is present outside of the nucleus of an atom.

1. It is present inside the nucleus of an atom.

1. It is present inside the nucleus of an atom.

2. Carry negative charge.

2. Carry positive charge

2. It is neutral.

3. Its weight is negligible.

3. It weighs around 2000 times as mass of electrons.

3. Weight is the same as a proton.


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.

  1. It fails to explain the stability of an atom.

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

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

  4. 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.

Ans:


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: 

Thomson’s Model

Rutherford’s Model

Bohr’s Model

1. According to this mode positively and negatively charged ions are embedded throughout the atom.



1. This model explained that all the positive ions are embedded in the nucleus and negative ions revolve around it.



1. Electron or negatively charged particles move around in a fixed circular path called the orbit. There is no energy generation in the electron revolution.


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.

Ans: 

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 ] 

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

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

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

$1620=2 y+1600$

$1620-1600=2 y$

20=2 y

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

y=10

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


X

Y

Protons

6

6

Neutrons

6

8

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

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

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. 

Ans: False

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.

Ans: False


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

  1. Atomic nucleus

  2. Electron

  3. Proton

  4. Neutron

Ans: a) Atomic Nucleus


16. Isotopes of an element have 

  1. The same physical properties  

  2. Different chemical properties 

  3. Different number of neutrons

  4. 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: 

  1. 16

  2. 8

  3. 17

  4. 18

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? 

  1. 2, 8

  2. 8, 2, 1

  3. 2, 1, 8

  4. 2, 8, 1

Ans: Atomic number of sodium =  = Number of electrons 

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


19. Complete the following table.

Atomic Number

Mass Number

Number of Neutrons

Number of Proton

Number of Electrons

Name of the atomic species

9

-

10

-

-

-

16

32

-

-

-

Sulphur

-

24

-

12

-

-

-

2

-

1

-

-

-

1

0

1

1

-

Ans:

Atomic Number

Mass Number

Number of Neutrons

Number of Proton

Number of Electrons

Name of the atomic species

9

19

10

9

9

Fluorine

16

32

16

16

16

Sulphur

12

24

12

12

12

Magnesium

1

2

1

1

1

Deuterium

1

1

0

1

1

Protonium


Topics Covered in Class 9 Chapter 4 Science

List of Topics Covered in Class 9 Structure of The Atom

Topics

Subtopics

Charged Particles in Matter


The Structure of an Atom

Thomson’s Model, Rutherford’s Model, Bohr’s Model, Neutrns

How are Electrons Distributed in Different Orbits?


Valency


Atomic Number and Mass Number

Atomic number, Mass number

Isotopes

Isobars


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

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


  • Expert Curated: structure of the atom class 9 question answers revision notes crafted by subject experts, ensuring coverage of all crucial topics like how scientists proved the existence of subatomic particles within an atom. 

  • Simple and Precise Format: class 9 structure of atom question answers notes presented in a straightforward, precise, and easy-to-understand format, promoting clarity and efficient revision. The consecutive development of theories will make you understand how an atom stabilises its charges. 

  • Inclusion of Important Diagrams: The class 9 chapter 4 science features a list of key diagrams, enhancing conceptual understanding and aiding visual learners.

  • Illustrative Examples:  atomic structure class 9 concepts are reinforced with examples, providing practical applications to enhance comprehension of the underlying theories.


Important Study Material Links for Class 9 Chapter 4 Science


Conclusion

NCERT Solutions class 9 science ch 4 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 atom class 9 PDF's downloadable structure is 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 - Other Chapter-Wise Links 

The links for the other chapter-wise NCERT Solutions for Class 9 Science are given below.



Important Study Material Links for Class 9 Science

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 PDF for class 9 science chapter 4 question answers for free and start your preparation today.

2. Why Should You Prefer the NCERT Solutions for the Structure of the Atom Class 9 questions and answers? 

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

3. How can NCERT Solutions for Class 9 Chemistry Chapter 4 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 according to the class 9?

The structure of the atom class 9 question answers consist 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. Download the NCERT Solutions Class 9 Science Chapter 4 for similar solutions on the website.

5. Who discovered the atom according to the class 9 structure of atom question answers 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 from class 9, chapter 4 science.

The smallest unit present in any matter is an atom. It contains protons, electrons, and neutrons 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 the Vedantu website and mobile app.

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

In atomic structure class 9, 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 website.

8. What is Thomson’s model of an atom from the structure of the atom class 9 PDF?

According to 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. Students can refer to class 9 science chapter 4 question answers PDF to get all the solved answers for this chapter.

9. What are the important topics from the structure of the atom class 9 question answers?

The important topics from this chapter are:

  • Thomson’s Model

  • Rutherford’s Model of the atom

  • Bohr’s Model of the atom

  • Atomic Number

  • Atomic Mass