Electron

The electron is a fundamental subatomic particle that carries a negative electric charge. It is a spin ½ lepton that participates in electromagnetic interactions, and its mass is approximately 1 / 1836 of that of the proton. Together with atomic nuclei, which consist of protons and neutrons, electrons make up atoms. Their interaction with adjacent nuclei is the main cause of chemical bonding.

The discovery that the electron was a subatomic particle was made in 1897 by J.J. Thomson at the Cavendish Laboratory at Cambridge University, while he was studying cathode ray tubes. A cathode ray tube is a sealed glass cylinder in which two electrodes are separated by a vacuum. When a voltage is applied across the electrodes, cathode rays are generated, causing the tube to glow. Through experimentation, Thomson discovered that the negative charge could not be separated from the rays (by the application of magnetism), and that the rays could be deflected by an electric field. He concluded that these rays, rather than being waves, were composed of negatively charged particles he called "corpuscles". He measured their mass-to-charge ratio and found it to be over a thousand times smaller than that of a hydrogen ion, suggesting that they were either very highly charged or very small in mass.

Electrons have an electric charge of −1.602 × 10−19 C, a mass of 9.11 × 10−31 kg based on charge/mass measurements equivalent to a rest mass of about 0.511 MeV/c². The mass of the electron is approximately 1/1836 of the mass of the proton. The common electron symbol is e−. The electron is thought to be stable on theoretical grounds; the lowest known experimental upper bound for its mean lifetime is 4.6×1026 years.