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Definition of ELECTRON
: an elementary particle consisting of a charge of negative electricity equal to about 1.602 × 10−19 coulomb and having a mass when at rest of about 9.109 × 10−31 kilogram or about 1⁄1836 that of a proton
: an elementary particle consisting of a charge of negative electricity equal to about 1.602 × 10−19 coulomb and having a mass when at rest of about 9.109534 × 10−28 gram or about 1⁄1836 that of a proton
Lightest electrically charged subatomic particle known. It carries a negative charge (seeelectric charge), the basic charge of electricity. An electron has a small mass, less than 0.1% the mass of an atom. Under normal circumstances, electrons move about the nucleus of an atom in orbitals that form an electron cloud bound in varying strengths to the positively charged nucleus. Electrons closer to the nucleus are held more tightly. The first subatomic particle discovered, the electron was identified in 1897 by J. J. Thomson.