Experiments with a Crookes tube first demonstrated the particle nature of electrons. In this illustration, the profile of the Maltese-cross-shaped target is projected against the tube face at right by a beam of electrons.

The electron (symbol: e−) is a subatomic particle with a negative elementary electric charge.^[8] It is generally thought to be an elementary particlebecause it has no known components or substructure.^[2] An electron has a mass that is approximately 1/1836 that of the proton.^[9] The intrinsic angular momentum (spin) of the electron is a half-integer value in units of ħ, which means that it is a fermion. The antiparticle of the electron is called the positron; it is identical to the electron except that it carries electrical and other charges of the opposite sign. When an electron collides with a positron, both particles may be totally annihilated, producing gamma ray photons.

Electrons, which belong to the first generation of the lepton particle family,^[10] participate in gravitational, electromagnetic and weak interactions.^[11] Like all matter, they have quantum mechanical properties of both particles and waves, so they can collide with other particles and can be diffracted like light. However, experiments with electrons best demonstrate this duality because electrons have a tiny mass. Being fermions, no two electrons can occupy the same quantum state, in accordance with the Pauli exclusion principle.^[10]

British natural philosopher Richard Laming first hypothesized the concept of an indivisible quantity of electric charge to explain the chemical properties ofatoms 1838;^[4] Irish physicist George Johnstone Stoney named this charge 'electron' in 1891, and J. J. Thomson and his team of British physicists identified it as a particle in 1897.^[6][12][13]

Electrons play an essential role in many physical phenomena, such as electricity, magnetism, and thermal conductivity. An electron moving relative to an observer generates a magnetic field; external magnetic fields will deflect it. Electrons radiate or absorb energy in the form of photons when accelerated. Electrons bound to atomic nuclei made of protons and neutrons by the attractive Coulomb force compose atoms. However, electrons contribute less than 0.06% to an atom's total mass. The exchange or sharing of the electrons between two or more atoms is the main cause of chemical bonding.^[14]

Electrons may be created through beta decay of radioactive isotopes and in high-energy collisions, for instance when cosmic rays enter the atmosphere. Annihilation with positrons can destroy electrons, and electrons may be absorbed during nucleosynthesis in stars. Laboratory instruments are capable of containing and observing individual electrons as well as electron plasma, whereas dedicated telescopes can detect electron plasma in outer space. Electrons have many applications, including in electronics, welding, cathode ray tubes, electron microscopes, radiation therapy, lasers, gaseous ionization detectors and particle accelerators.