Gilbert Lewis. Portrait of the American chemist Gilbert Newton Lewis (1875-1946). In 1923 he published his important theories on chemical thermodynamics. During 1916-23 Lewis devised a theory of molecular bonds in which atoms were bound together by sharing pairs of electrons (a covalent bond). He broadened the definition of acids and bases to include molecules that were electron acceptors or donors. Molecules accepting electrons are called Lewis acids, while electron donors are known as Lewis bases. In 1933 he was the first person to make a sample of heavy water" in which all the molecules contained a heavy form of hydrogen (deuterium)."