The Lewis Theory
The scientist G.N. Lewis put forward a more elaborate theory regarding acids and bases. According to him, a Lewis acid is a species that can accept a pair of electrons from another species. He defined Lewis base as any species that can donate a pair of electrons to another species. For a thorough understanding of this concept, let's look at a typical Lewis acid-base reaction. The reaction between ammonia (NH3) and boron trichloride (BCl3) is shown:
In this reaction, the electron acceptor is boron trichloride (Lewis acid) and the electron donor is ammonia (Lewis base). The new bond that is formed between the acid and the base is a coordinate covalent bond.