Introduction Growing up, we used to think that any substance that burns is an acid, until we learnt about acids, bases and salts in our foundational chemistry class. It was then clear to us that there is more to acids than corrosivity, and not every substance that is corrosive, is an acid. Definition The definitions of an acid is based on three different concepts of acid-base reactions, namely the Lewis, Brønsted-Lowry and Arrhenius concepts. Lewis Acids According to G. N. Lewis, in acid-base reactions, the reactants undergo co-ordinate covalent bonding, in which one reacting species has the ability to accept a lone pair of electrons, while the other can readily donate a lone pair of electrons. A Lewis acid is an electron pair acceptor, because it has an empty orbital. Examples are H+, H3O+, Cu2+, Fe3+. Brønsted -Lowry Acids According to J. H. Brønsted and M. Lowry, an acid-base reaction involves the transfer of proton from one of the reactants to the other. A Brønsted-Low
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