Lewis Theory

According to Brønsted-Lowry theory, only a species containing at least one hydrogen atom has the potential to act as an acid in a reaction.  Lewis theory is an attempt to extend the concept of acidity beyond species containing hydrogen.  According to Lewis theory, in a reaction, a species that accepts a pair of electrons to form a new covalent bond is an acid, and a species that contribute s a pair of electrons toward a new covalent bond is a base.

eg. 1:



In this reaction, BF3 accepts a pair of electrons from F ¯ to form a new covalent bond and, therefore, acts as an acid;  F ¯ contributes a pair of electrons toward a new covalent bond with BF3 and, therefore, acts as a base.

In a reaction a species that acts as an acid according to Lewis theory is called a Lewis acid and a species that acts as a base a Lewis base.



eg. 2:



Print Friendly