Fundamental particles which constitute an atom are electrons, protons and neutrons.

Electron is a subatomic particle having a unit negative charge (-1.602 x 10^-19coulombs) and a mass (9.11 x 10^-31 kg) which is 1/1837 of that of a hydrogen atom.

Proton is a subatomic particle of an atom having a unit positive charge (1.602x10^-19 coulombs) and a mass (1.67x 10^-27 kg) which is practically the same as that of a hydrogen atom.