Discovery of electron

Historical Experiment: Discovery of the Electron

Discoverer: J.J. Thomson

The electron is a tiny negatively charged particle that is a part of every atom. The discovery of the electron marked a major turning point in the advancement of scientific knowledge. The person who discovered the electron was a British scientist named J.J. Thomson in the year 1897.

The Cathode Ray Experiment

J.J. Thomson made his discovery while working with a piece of equipment called a cathode ray tube. This is a sealed glass tube from which most of the air is removed. Inside the tube, there are two metal plates called electrodes—one positive and one negative. Upon applying a high voltage, an invisible beam known as a cathode ray moves from the negatively charged electrode (cathode) toward the positively charged electrode (anode).

Key Observations:

• The beam was deflected by electric and magnetic fields, which showed it was made of particles and not light.
• The particles were always the same, no matter what material was used for the electrodes or the gas inside the tube.
• Thomson calculated the mass-to-charge ratio of the particles and discovered that they were far tinier than atoms.

From these observations, J.J. Thomson concluded that the beam was made of negatively charged particles, which he called corpuscles. These were later named electrons.

This experiment proved that atoms are not indivisible, as was earlier believed. Instead, atoms are made up of smaller particles—starting with the electron.

Importance:

Thomson’s discovery changed the way scientists understood the structure of the atom. It led to further research and eventually to the development of modern atomic models.