Lewis acids and bases studied chemical bonding. In 1923, Lewis wrote "An acid substance is one which can employ an electron lone pair from another molecule in completing the stable group of one of its own atoms." The Brønsted–Lowry acid–base theory was published in the same year. The two theories are distinct but complementary. A Lewis base is also a Brønsted–Lowry base, but a Lewis acid doesn't need to be a Brønsted–Lowry acid. The classification into hard and soft acids and bases (HSAB theory) followed in 1963. The strength of Lewis acid-base interactions, as measured by the standard enthalpy of formation of an adduct
Chemical nomenclature of technical terms used in chemistry. Similar compendia exist for biochemistry (the "White Book", in association with the IUBMB), analytical chemistry (the "Orange Book"), macromolecular chemistry (the "Purple Book") and clinical chemistry (the "Silver Book"). These "color books" are supplemented by shorter recommendations for specific circumstances that are published periodically in the journal "Pure and Applied Chemistry". The primary function of chemical nomenclature is to ensure that a spoken or written chemical name leaves no ambiguity concerning which chemical compound the name refers to: each chemical name should refer to a single substance. A less important aim is to ensure