Atoms, the fundamental building blocks of matter, are composed of charged particles. This discovery was crucial for understanding the nature of matter and its electrical properties.

Discovery of Sub-Atomic Particles

Electrons

Discovery: The electron was discovered by J.J. Thomson in 1897 through experiments with cathode rays. He identified the electron as a negatively charged particle within the atom.

Properties: Electrons are represented as ‘e⁻’. They have a very small mass, approximately 1/2000th of the mass of a proton, and carry a negative charge of -1 unit.

Protons

Discovery: Before the electron was discovered, E. Goldstein in 1886 observed positively charged particles in a gas discharge tube, which he called canal rays. This led to the discovery of the proton.

Properties: Protons are represented as ‘p⁺’. They have a positive charge of +1 unit, which is equal in magnitude but opposite in sign to the charge of an electron. The mass of a proton is taken as one atomic mass unit (u), making it about 2000 times heavier than an electron.