Named after G. N. Lewis, Lewis acid and base were first mentioned in 1923. Lewis acid-base theory considers the electron donor as a base and electron acceptor as an acid As an extension of Bronsted-Lowry acid-base theory, it is of fundamental importance in both inorganic chemistry and organic chemistry. Lewis adduct, known as the product of Lewis acid-base reaction, is usually considered stable if the reaction follows the rule of the reaction between hard and soft acid and base, which means the hard acid reacts with a hard base and soft acid reacts with a soft base. 23