Lewis Acid-Base Reaction Definition

A Lewis acid-base reaction is a chemical reaction that forms at least one covalent bond between an electron pair donor (Lewis base) and an electron pair acceptor (Lewis acid). The general form of a Lewis acid-base reaction is:

A⁺ + B^- → A-B

where A⁺ is an electron acceptor or Lewis acid, B^- is an electron donor or Lewis base, and A-B is a coordinate covalent compound.

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Bronsted Lowry Theory of Acids and Bases

By Anne Marie Helmenstine, Ph.D.

Significance of Lewis Acid-Base Reactions

Most of the time, chemists apply the Brønsted acid-base theory (Brønsted-Lowry) in which acids act as proton donors and bases are proton acceptors. While this works well for many chemical reactions, it doesn't always work, particularly when applied to reactions involving gases and solids. The Lewis theory focuses on electrons rather than proton transfer, allowing for prediction of many more acid-base reactions.

Example Lewis Acid-Base Reaction

While Brønsted theory cannot explain the formation of complex ions with a central metal ion, Lewis acid-base theory sees the metal as the Lewis Acid and the ligand of the coordination compound as a Lewis Base.

Al³⁺ + 6H₂O ⇌ [Al(H₂O)₆]³⁺

The aluminum metal ion has an unfilled valence shell, so it acts as an electron acceptor or Lewis acid. Water has lone pair electrons, so it can donate electrons to serve as the anion or Lewis base.