Lewis Acid-Base Theory

Lewis acid-base theory defines an acid as any species capable of accepting a pair of electrons and a base as any species capable of donating a pair of electrons, a broader definition than earlier acid-base theories that required the transfer of a proton. American chemist Gilbert N. Lewis proposed the theory in 1923, the same year Johannes Bronsted and Thomas Lowry independently proposed their own proton-based definition, and Lewis's electron-pair framework is generally regarded as the most general of the major acid-base theories because it does not require the presence of hydrogen at all. Under Lewis's definition, the reaction between a Lewis acid and a Lewis base forms a coordinate covalent bond, called a dative bond, in which both electrons of the shared pair originate from the base; boron trifluoride reacting with ammonia is a standard example, since boron trifluoride has an incomplete octet capable of accepting an electron pair while ammonia's nitrogen atom has a lone pair to donate. The theory extended acid-base chemistry beyond aqueous, proton-transfer reactions to a wide range of reactions in organic and inorganic chemistry, including many reactions involving metal ions and their ligands.