Electrons have the smallest electrical charge and when they move, they generate an electric current. Because the electrons of an atom defines its attraction to other atoms, electrons play a fundamental part in chemistry.
Electrons in practice
Classification of electrons
The word "particle" is somewhat misleading however, because quantum mechanics show that electrons sometimes behave like a wave, e.g. in the double-slit experiment: this is called wave-particle duality.
Properties and behavior of electrons
The motion of the electron about the nucleus is a somewhat controversial topic. The electron does not exhibit motion in the physical sense - it does not "float"; rather, it seems to appear in and out of existence, at various points around the nucleus (of course, 90% of the time the electron can be found in its designated orbital). A simple analogy would be a firefly, in a dark room, lighting up at various points about a central light source - it can light up anywhere, but it is most likely to appear closer to the source than otherwise. By this analogy, the electron can "appear" anywhere, and while its next location can be generalized, where it will pop up exactly can never be known. For this reason many scientists believe that the motion of the electron can never be fully understood.
So-called "static electricity" is not a flow of electrons. More correctly called a "static charge", it refers to a body that has more or fewer electrons than are required to balance the positive charge of the nuclei. When there is an excess of electrons, the object is said to be "negatively charged". When there are fewer electrons than protons, the object is said to be "positively charged". When the number of electrons and the number of protons are equal, the object is said to be electrically "neutral".
The electron is an elementary particle -- that means that it has no substructure (at least, experiments have not found any so far, and there is good reason to believe that there is not any). Hence, it is usually described as point-like, i.e. with no spatial extension. (However, if one gets very near an electron, one notices that its properties (charge and mass) seem to change. This is an effect common to all elementary particles: the particle influences the vacuum fluctuations in its vicinity, so that the properties one observes from far away are the sum of the bare properties and the vacuum effects -- see renormalization.)
There is a physical constant called the classical electron radius, with a value of 2.8179 × 10−15 m. Note that this is the radius that one could infer from its charge if the physics were only described by the classical theory of electrodynamics and there were no quantum mechanics (hence, it is an outdated concept, that, however, sometimes still proves useful in calculations).
Electrons in the Universe
It is believed that the number of electrons that would fit in the known universe is 10130 (that is, 1 followed by 130 zeros.)
Electrons in everyday life
The electric currents that power domestic equipment are all caused by electrons in motion. The cathode ray tube of a television set uses an electron beam in a vacuum to generate the image on the phosphorescent screen. The quantum behavior of electrons is used in semiconductor devices such as transistors.
Electrons in industry
Electrons in the laboratory
The spin of an electron is observed in the Stern-Gerlach experiment.
Use of electrons in the laboratory
Electrons in theory
In quantum mechanics, the electron is described by the Dirac Equation. In the Standard Model of particle physics, it forms a doublet in SU(2) with the electron neutrino, as they interact through the weak interaction. The electron has two more massive partners, with the same charge but different masses: the muon and the tauon.
The antimatter counterpart of the electron is its antiparticle, the positron. The positron has the same amount of electrical charge as the electron, except that the charge is positive. It has the same mass and spin as the electron. When an electron and a positron meet, they may annihilate each other, giving rise to two gamma-ray photons, each having an energy of 0.511 MeV (511 keV). See also Electron-positron annihilation.
Electrons are also a key element in electromagnetism, an approximate theory that is adequate for macroscopic systems.
The electron was discovered by J.J. Thomson in 1897 at the Cavendish Laboratory at Cambridge University, while studying "cathode rays". Influenced by the work of James Clerk Maxwell, and the discovery of the X-ray, he deduced that cathode rays existed and were negatively charged "particles", which he called "corpuscles".