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An electron is a very small piece of matter. Its symbol is −, and it was discovered by J. J. Thomson in 1897.

The electron is a subatomic particle. Every atom is made of some electrons that surround the nucleus of the atom. An electron can also be separate from any atom. It is believed to be an elementary particle because it cannot be broken down into anything smaller. Its electric charge is negative. Electrons have very little mass (little weight) so very little energy is needed to move them fast. They may move almost at the speed of light, for instance, as beta particles, and in the inner electron shells of elements with a large atomic number.