Elementary Particle (see Elementary Particles) carrying a unit charge of negative Electricity. An Atom consists of a small, dense, positively charged nucleus surrounded by
electrons that whirl about it in orbits, forming a cloud of charge. Ordinarily there
are just enough negative electrons to balance the positive charge of the nucleus,
and the atom is neutral. If electrons are added or removed, a net charge
results, and the atom is said to be ionized (see Ion). Atomic electrons are responsible for the chemical properties of Matter (see Valence). The electron was discovered in 1897 by Thomson, Joseph John, who showed that cathode rays are composed of electrons. The electron is the
lightest known particle having a non-zero Rest Mass. The positron, the electron's Antiparticle (see Antimatter), was discovered in 1932.