Class 9 NCERT Solutions Structure of the Atom

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Class 9 NCERT Solutions Structure of the Atom - NCERT Solutions prepared for CBSE students by the best teachers in Delhi. 

Class IX Science

 Chapter 4 – Structure of the Atom

Question 1:

What are canal rays?


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?


An electron is a negatively charged particle, whereas a proton is a positively charged particle. The magnitude of their charges is equal. Therefore, an atom containing one electron and one proton will not carry any charge. Thus, it will be a neutral atom.

Question 3:

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


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.

Question 4:

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


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

Question 5:

Name the three sub-atomic particles of an atom.


The three sub-atomic particles of an atom are:

(i) Protons

(ii) Electrons, and

(iii) Neutrons

Question 6:

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


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.


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