This theory is based on the concept of electron pairs and chemical bonding, rather than on the traditional concept of hydrogen ions (H+) and hydroxide ions (OH-) as defined by the Arrhenius theory.

In the Lewis theory, an acid-base reaction is viewed as the transfer of an electron pair from the base to the acid. The acid, which is electron-deficient, accepts the electron pair from the base, which is electron-rich. This results in the formation of a covalent bond between the acid and the base.

Some examples of acids and bases according to the Lewis theory include:

- Acids: BF3, AlCl3, H+, CO2, SO3

- Bases: NH3, H2O, OH-, CH3COO-, pyridine

The Lewis theory is particularly useful in understanding the behaviour of acids and bases in non-aqueous solvents, where the traditional Arrhenius theory may not be applicable. It also provides a more general framework for understanding acid-base reactions, as it encompasses a wider range of reactions than the Arrhenius theory.

Despite the usefulness of the Lewis theory, the Arrhenius theory is still widely used, particularly in introductory chemistry courses, due to its simplicity and its focus on the behaviour of acids and bases in aqueous solutions.