Definition of Electron

(Physics & Chem.) one of the fundamental subatomic particles, having a negative charge and about one thousandth the mass of a hydrogen atom. The electron carries (or is) a natural unit of negative electricity, equal to 3.4 x 10^-10 electrostatic units, and is classed by physicists as a lepton. Its mass is practically constant at the lesser speeds, but increases due to relativistic effects as the velocity approaches that of light. Electrons are all of one kind, so far as is known. Thus far, no structure has been detected within an electron, and it is probably one of the ultimate composite constituents of all matter. An atom or group of atoms from which an electron has been detached has a positive charge and is called a cation.