Structure Of Atom NCERT Class 11 Chemistry Discovery of Electron

Class 11 in this class you are going to learn about the Discovery of electrons. It is very beneficial for students since it adds them to scoring high marks in examinations. These NCERT books provide solution modules with various shortcut hints and practical examples to explain all the exercises. As a student, you will learn detailed information about the discovery of electrons.

J.J Thomson discovered the electron by conducting an experiment Called Cathode ray tube

In this experiment, he used a Crookes tube, which was a 60cm long glass tube and had a small tube attached. This small tube vacuum pump was attached, it has two metal plates which are attached to the battery by wires.

The tube with gas at atmospheric pressure. when the current was passed at high voltage 10,000 volts the following observations were made:

Here you are going to learn in detail and step by step and help you to understand more effectively.

  1. When the current was passed through a gas at 1 atmospheric pressure and it is a very high voltage, nothing happened. There is no visible effect seen.
  2. Then the pressure of the gas was reduced by pumping the air out, using a vacuum pump. The pressure was reduced to 10 – 2atm, then on passing current it was observed, the whole tube started glowing green.
  3. Further, the pressure was reduced to 10 – 4It was observed the whole glow vanished, but it was observed that at the end of the tube [Anode Side] there was a faint green glow seen.

To confirm the faint glow anode was made perforated, and a zinc sulfide screen (fluorescent material) was placed behind it.

When the current was passed through the same conditions, it also started glowing green. This confirmed that under these conditions some rays are emitted through [cathode] and were traveling towards [anode]. Those rays were called cathode rays and found to consist of negatively charged particles called electrons.

Properties of cathode rays

They are found to travel in a straight line. This property was examined by performing an activity where the path of the object is placed. When they hit it, they showed the shadow of the object as shown below points :

  • Cathode rays are formed of material particles.
  • They charged negatively, this property was concluded by performing an activity where both electric and magnetic fields are applied. So, they deflected towards the positive plate and in presence of magnetic flux, they deflected towards the north pole.
  • When they strike some metal surface, they heat. So, it has been concluded they will also produce a heating effect.
  • They cause ionization of gas through which it passes.
  • They produce x-rays when struck against tungsten etc. like hard material
  • They can make fluorescent material glow when exposed to some fluorescent material.
  • They affect the photographic plate.
  • They have a penetrating effect.

From the above properties and experiment, it had been concluded that cathode rays are made from negatively charged particles called electrons. Further experiments were administered so as to understand the charge and mass of the electron. It was found to be:

  • Charge :1.6 x 10-19C
  • Mass 9.1 x 10-31kg

We can define an electron as

“An elementary particle that negatively charges of magnitude 1.6 x 10-19C and mass adequate to 9.1 x 10-31


So in this topic, we have learned about the atom and its structure. In all the atoms, physics is an important part of everyday lives. Whereas everywhere people look there is an atom physics yes it is all around us.and the universe is made of matter and matter is made of atoms. However, it is beneficial to our as the power to influence society.

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