• Dalton's atomic theory suggested that atoms are indivisible.

  • Atoms can not be divided further.

  • However, later it was found that atoms contained even smaller particles like electrons and protons.

  • Different scientists proposed different models of an atom to explain the structure of an atom.

1. structure of an atom-Teachoo.png

 

CHARGED PARTICLES OF MATTER

 

  • Before the discovery of any model of an atom

  • E.Goldstein discovered the presence of a new radiation.

  • Electricity was passed through the discharge tube at high voltage through a gas at low pressure taken in a tube.

  • These rays were positively charged raditions called canal rays .

  • It was only because of these rays that charged subatomic particles (particles of an atom) were discovered .

2. anode-Teachoo.png

 

The sub-particles discovered were: -

 

  1. Protons (denoted by 'p+')

 

  1. Electrons (denoted by ‘e-’)

 

Protons

Electrons

Protons are positively charged particles.

Electrons are negatively charged particles.

As estimated by the scientists, a proton is about 2000 times heavier than an electron and weighed about 1 atomic mass unit

Mass of an electron was very less as compared to a proton.

Charge on a proton was +1

Charge on an electron was -1

It is denoted by " p+ "

It is denoted by " e- "

  1. Class 9
  2. Chapter 4 Class 9 - Structure of Atom (Term 2)

About the Author

CA Maninder Singh's photo - Founder at Teachoo
CA Maninder Singh
CA Maninder Singh is a Chartered Accountant for the past 11 years and a teacher from the past 11 years. He teaches Science, Accounts and English at Teachoo