Proton Acids, Lewis Acids, Hard Acids, Soft Acids and Superacids

Although the terms acid and base have been in use since the early days of chemistry, the meaning of these terms has undergone considerable modification through the centuries and continues even today with the recent introduction of new terms such as hard acid, soft acid and superacid. It is the purpose of this chapter to consider some of the classic definitions of the terms acid and base and also some of the more recent developments of our ideas concerning acids and bases [1].