What characterizes a Lewis acid?

A Lewis acid is characterized by its ability to accept an electron pair from a Lewis base during a chemical reaction. This means that a Lewis acid is defined based on its electronic properties rather than its ability to donate protons or hydrogen ions. The concept of Lewis acids and bases expands the traditional acid-base theory to include species that participate in electron pair transfers, which is essential in many chemical reactions, particularly those involving coordination compounds and organic reactions.

The other choices focus on definitions more aligned with the Brønsted-Lowry theory of acids and bases, where an acid is defined primarily by its ability to donate protons (hydrogen ions) or accept them. In contrast, the Lewis definition highlights the fundamental role of electron pairs in chemical bonding and reactivity. This broader perspective is crucial when considering various reactions in organic and inorganic chemistry, thus understanding Lewis acids lays the groundwork for deeper comprehension of reaction mechanisms and interactions in various chemical systems.