Electron, lightest stable subatomic particle known. It carries a negative charge, which is considered the basic unit ofelectric charge The rest masso f the electron is 9.10938356 × 10−31 kg, which is only 1/1,836the mass of a proton. An electron is therefore considered nearly massless in comparison with a proton or a neutron, and the electron mass is not included in calculating the mass numbers of an atom.
