Electron - sustainable elementary particle with a minimum electric charge. The electron mass is 9,108·10-28 ,
Electron - the most important part of the atoms of all substances (see Atom). The number of electron shells of atoms depends on the location of the element in the periodic system of chemical elements and is equal to the number of protons in the nucleus or to a serial number of an element, or slightly less for ionized atom.
Electrons can revolve around the nucleus only by well defined orbits. The electron transitions from one orbit to another occur with emission or absorption of atom certain portions (quanta) of energy. During the transition of the electron on the orbit, closer to the nucleus, atom emits visible and invisible radiation. For reverse transition the atom must absorb the appropriate amount of energy.
Electrons are also found in a free state, out of atoms. The directional flow of electrons in matter is an electric current. Electrons can be accelerated to high energies. Beams of such electrons are widely used in science and engineering (see Electron radiation).