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# NCERT solutions for Class 9 Science chapter 4 - Structure of the Atom

## Chapter 4: Structure of the Atom

#### Chapter 4: Structure of the Atom solutions [Page 47]

Q 1 | Page 47

What are canal rays?

Q 2 | Page 47

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

#### Chapter 4: Structure of the Atom solutions [Page 49]

Q 1 | Page 49

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

Q 2 | Page 49

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

Q 3 | Page 49

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

Q 4 | Page 49

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?

#### Chapter 4: Structure of the Atom solutions [Page 49]

Q 1 | Page 49

Name the three sub-atomic particles of an atom.

Q 2 | Page 49

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

#### Chapter 4: Structure of the Atom solutions [Page 50]

Q 1 | Page 50

Write the distribution of electrons in carbon and sodium atoms?

Q 2 | Page 50

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

#### Chapter 4: Structure of the Atom solutions [Page 52]

Q 1 | Page 52

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

#### Chapter 4: Structure of the Atom solutions [Page 52]

Q 1 | Page 52

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?

Q 2 | Page 52

With the help of given Table 4.1, find out the mass number of oxygen.

Table 4.1: Composition of Atoms of the First Eighteen Elements with Electron Distribution in Various Shells

 Name of Element Symbol Atomic Number Number of protons Number of Neutrons Number of Electrons Distribution of Electrons Valency K L M N Hydrogen H 1 1 - 1 1 - - - 1 Helium He 2 2 2 2 2 - - - 0 Lithium Li 3 3 4 3 2 1 - - 1 Beryllium Be 4 4 5 4 2 2 - - 2 Boron B 5 5 6 5 2 3 - - 3 Carbon C 6 6 6 6 2 4 - - 4 Nitrogen N 7 7 7 7 2 5 - - 3 Oxygen O 8 8 8 8 2 6 - - 2 Fluorine F 9 9 10 9 2 7 - - 1 Neon Ne 10 10 10 10 2 8 - - 0 Sodium Na 11 11 12 11 2 8 1 - 1 Magnesium Mg 12 12 12 12 2 8 2 - 2 Aluminium Al 13 13 14 13 2 8 3 - 3 Silicon Si 14 14 14 14 2 8 4 - 4 Phosphorus P 15 15 16 15 2 8 5 - 3.5 Sulphur S 16 16 16 16 2 8 6 - 2 Chlorine Cl 17 17 18 17 2 8 7 - 1 Argon Ar 18 18 22 18 2 8 8 0

#### Chapter 4: Structure of the Atom solutions [Page 53]

Q 1 | Page 53

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

Q 2 | Page 53

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

#### Chapter 4: Structure of the Atom solutions [Pages 54 - 55]

Q 1 | Page 54

Compare the properties of electrons, protons and neutrons.

Q 2 | Page 54

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

Q 3 | Page 54

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

Q 4 | Page 54

Describe Bohr’s model of the atom.

Q 5 | Page 54

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

Q 6 | Page 54

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

Q 7 | Page 54

Define valency by taking examples of silicon and oxygen.

Q 8.1 | Page 55

Explain Atomic number with examples.

Q 8.2 | Page 55

Explain Mass number with examples.

Q 8.3 | Page 55

Explain Isotopes with examples.

Q 8.4 | Page 55

Explain Isobars with examples.

Q 8.5 | Page 55

Give any two uses of isotopes

Q 9 | Page 55

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

Q 10 | Page 55

If bromine atom is available in the form of, say, two isotopes ""_35^79Br (49.7%)" and """_35^81Br (50.3%), calculate the average atomic mass of bromine atom.

Q 11 | Page 55

The average atomic mass of a sample of an element X is 16.2 u. What are the percentages of isotopes ""_8^16X" and """_8^18X  in the sample?

Q 12 | Page 55

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

Q 13 | Page 55

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

 X Y Protons 6 6 Neutrons 6 8

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

Q 14.1 | Page 55

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

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

• True

• False

Q 14.2 | Page 55

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

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

• True

• False

Q 14.3 | Page 55

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

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

• True

• False

Q 14.4 | Page 55

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

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

• True

• False

Q 15 | Page 55

Put tick (✓) against correct choice and cross (×) against wrong choice in following question.

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

(a) Atomic nucleus

(b) Electron

(c) Proton

(d) Neutron

Q 16 | Page 55

Put tick (✓) against correct choice and cross (×) against wrong choice in following question.

Isotopes of an element have

(a) the same physical properties

(b) different chemical properties

(c) different number of neutrons

(d) different atomic numbers

Q 17 | Page 55

Put tick (✓) against correct choice and cross (×) against wrong choice in following question.

Number of valence electrons in Cl ion are:

(a) 16

(b) 8

(c) 17

(d) 18

Q 18 | Page 55

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

Q 19 | Page 55

Complete the following table.

 Atomic number Mass number Number of Neutrons Number of protons Number of electrons Name of the Atomic species 9 - 10 - - - 16 32 - - - Sulphur - 24 - 12 - - - 2 - 1 - - - 1 0 1 0 -

## NCERT solutions for Class 9 Science chapter 4 - Structure of the Atom

NCERT solutions for Class 9 Science chapter 4 (Structure of the Atom) include all questions with solution and detail explanation. This will clear students doubts about any question and improve application skills while preparing for board exams. The detailed, step-by-step solutions will help you understand the concepts better and clear your confusions, if any. Shaalaa.com has the CBSE Science Textbook for Class 9 solutions in a manner that help students grasp basic concepts better and faster.

Further, we at Shaalaa.com are providing such solutions so that students can prepare for written exams. NCERT textbook solutions can be a core help for self-study and acts as a perfect self-help guidance for students.

Concepts covered in Class 9 Science chapter 4 Structure of the Atom are Eugen Goldstein, Concept of Electron, Concept of Proton, Structure of Atom Numericals, Concept of Isobars, Concept of Isotopes, Mass Number, Atomic Number, Valency, Concept of Electrons Distributed in Different Orbits (Shells), Structure of an Atom - Neutrons, Structure of an Atom - Bohr’S Model of Atom, Structure of an Atom - Rutherford’S Model of an Atom, Structure of an Atom - Thomson’S Model of an Atom, Charged Particles in Matter, Structure of Atom Introduction.

Using NCERT Class 9 solutions Structure of the Atom exercise by students are an easy way to prepare for the exams, as they involve solutions arranged chapter-wise also page wise. The questions involved in NCERT Solutions are important questions that can be asked in the final exam. Maximum students of CBSE Class 9 prefer NCERT Textbook Solutions to score more in exam.

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