Atoms were thought to be indivisible. They were thought to be the smallest unit . Through various experiments scientists concluded that an atom consists of even smaller particles called sub atomic particles. An atom consists of three subatomic particles namely electrons, protons and neutrons.
Electrons are the negative charged particles, very tiny, have negligible mass. Protons are the positively charged particles, have greater mass than an electron, and are found in the center of an atom inside the nucleus. Neutrons are the neutral particles, have mass comparable to proton, neutrons are located inside the the nucleus.