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Symbol e or e{TAG(tag=>sup)}-{TAG}. An elementary particle which is a constituent of all atoms, occupying an atomic orbital around the nucleus. It was discovered by J. J. Thomson in 1897. The electron is a lepton and therefore a fermion, with spin quantum number 1/2. It has a mass of 9.109Ð¥10{TAG(tag=>sup)}-31{TAG} kg, more conveniently written as a rest mass of 0.5110 MeV/c{TAG(tag=>sup)}2{TAG} for the purpose of high-energy physics. It carries a charge of -1.602 Ð¥ 10{TAG(tag=>sup)}-19{TAG}C. A vast amount of solid state physics concerns the behaviour of electrons. Electrons are responsible for carrying electric current (and heat) in metals; since the charge is negative the electrons flow in the opposite direction to the conventional electric current. The behaviour of electrons in the presence of more than one nucleus is the essence of all chemistry (See chemical bonding). Electron transfer from one substance to another constitutes a redox reaction. Movement of electron pairs constitutes a reaction between Lewis acids and bases (See Lewis theory).See free electron; Appendix table 2.  



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