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Electron, negatively charged particle found in an atom. Electrons, along with neutrons and protons, comprise the basic building blocks of all atoms. The electrons form the outer layer or layers of an atom, while the neutrons and protons make up the nucleus, or core, of the atom. Electrons, neutrons, and protons are elementary particles—that is, they are among the smallest parts of matter that scientists can isolate. The electron carries a negative electric charge of –1.602 x 10-19 coulomb and has a mass of 9.109 x 10-31 kg.

Electrons are responsible for many important physical phenomena, such as electricity and light, and for physical and chemical properties of matter. Electrons form electric currents by flowing in a stream and carrying their negative charge with them. All electrical devices, from flashlights to computers, depend on the movement of electrons. Electrons also are involved in creating light. The electrons in the outer layers of the atom sometimes lose energy, emitting the energy in the form of light. Because electrons form the outer layers of atoms, they are also responsible for many of the physical and chemical properties of the chemical elements. Electrons help determine how atoms of an element behave with respect to each other and how they react with atoms of other elements.

Fraser, Gordon, B.Sc., ARCS, DIC, Ph.D.

Editor, CERN Courier, CERN European Laboratory for Particle Physics. Co-author of "Search for Infinity", author of "The Quark Machine", editor of Particle Century.