Chapter 2 - Atomic Structure

Comprehensive Questions & Answers for Class 9 Chemistry (Punjab Board)

Class 9 Chemistry Punjab Board
Q1
Answer:

Almost all mass of an atom is concentrated in its nucleus.

Reason:

  • Although the nucleus is less than one hundred thousandth (1/100,000) of the size of an atom, it contains more than 99.9% of the mass of an atom.
  • An atom contains three subatomic particles: electron, proton and neutron.
  • The nucleus contains the subatomic particles protons and neutrons.
  • The mass of the nucleus is the sum of the masses of protons and neutrons, which are located at the centre of the atom.
  • Electrons present outside the nucleus have negligible mass.

Therefore, almost all the mass of an atom is concentrated in its nucleus.

Q2
Answer:

Elements are different from one another.

Reason:

  • The number of protons in an atom define the feature of atom.
  • The proton number is equal to atomic number.
  • Each element has different atomic number.
  • These properties makes one element differs from one another.
Q3
Answer:

Solution:

Given:

  • Mass number = A = 210

  • Atomic number = Z = 83

To find:

Number of neutrons = ?

Calculation:

Number of neutron = mass number − atomic number

So, there are 127 neutrons in ²¹⁰₈₃Bi

Q4
Answer:

Reason:

  • Tritium is a radioactive element.
  • Tritium has unstable nucleus.
  • It contains two neutrons and one proton which makes its nucleus unstable.
  • It decays into Helium-3 by emitting beta radiation, making it radioactive isotope.

Nuclear Equation:

³₁H → ³₂He + ⁰₋₁e

Tritium → Helium → Beta particle

Q5
Answer:

Absorption of Energy:

An atom absorbs energy when electrons in lower energy level move to higher energy level from an external source like heat or light.

Emission of Energy:

An atom emits energy when electrons in higher energy level jumps into lower energy level by releasing the absorbed energy in form of light or other types of radiations.