The concept of Lewis acid and Lewis base is one of acids and bases, which is independent of the idea of protons. developed this idea in the early 20th century. In this concept, a Lewis acid can accept and bind electrons. Lewis acid is a substance that accepts two electrons to form a covalent bond. A Lewis base is a substance that gives two electrons in the bonding. A Lewis acid together with a Lewis base will react to make a compound called a Lewis adduct.