Atom or molecule that in a chemical reaction seeks an atom or molecule containing an electron pair available for bonding or the negative end of a polar molecule (see covalent bond; electric dipole). In the Lewis electron theory (see acid-base theory) advanced by the U.S. chemist Gilbert Lewis (1875–1946) in 1923, electrophiles are by definition Lewis acids. Examples include the hydronium ion (H₃O⁺), boron trifluoride (BF₃), and the halogens fluorine, chlorine, bromine, and iodine in molecular form. Seealso acid; nucleophile.

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