ion Any atom or molecule containing an unequal number of electrons and protons and therefore carrying a net positive or negative charge. A positive ion remains if an electron is removed, for example, by being struck by a photon or fast charged particle of sufficient energy to overcome the binding energy of that electron. Positive ions are used in ion propulsion. Related categories • ATOMIC AND NUCLEAR PHYSICS PHYSICAL CHEMISTRY Also on this site: Encyclopedia of Alternative Energy & Sustainable Living Encyclopedia of History Transport Concepts & Designs (partner site) |