An electron is a negatively charged elementary particle; it is a constituent of all atoms. The electrons in each atom surround the nucleus in groupings called shells; in a neutral atom the number of electrons is equal to the number of protons in the nucleus. This electron structure is responsible for the chemical properties of the atom; chemical interactions take place between the outer electrons of atoms.

Electrons have an electrical charge and when they move, they generate an electric current. Because the electrons of an atom determine the way in which it interacts with other atoms, they play a fundamental part in chemistry.

They were discovered by J J Thomson in 1897 through studying cathode rays (now called electron beams) in electric and magnetic fields. A heated wire filament can be made to emit electrons, and if this is done in a vacuum their paths can be controlled by electric or magnetic fields. Such beams of electrons are used to operate television picture tubes and electron microscopes.

The electron is a lightweight fundamental subatomic particle that carries a negative electric charge. The electron is a spin-1/2 lepton, does not participate in strong interactions and has no substructure. Together with atomic nuclei, electrons make up atoms; they are responsible for chemical bonding. The flow of electricity in solid conductors is primarily due to the movement of electrons.