What characterizes an acid according to Lewis theory?

According to Lewis theory, an acid is characterized as an electron pair acceptor. This definition arises from Lewis's broader perspective on acid-base reactions, which focuses on the transfer of electron pairs rather than protons, which is the focus of Brønsted-Lowry theory.

In this context, an acid can accept a pair of electrons from a base (which is an electron pair donor) to form a new bond. This interaction is key in various chemical reactions, including those involving coordination compounds and mechanisms that do not fit classical definitions.

For instance, metal ions, which can effectively accept electron pairs, serve as classic examples of Lewis acids. They are able to coordinate with electron-rich species, illustrating the principle that the interaction is governed by the acceptance of electron pairs, rather than proton transfer alone. This concept allows for a more inclusive understanding of acid-base chemistry, especially in complex systems not adequately described by other theories.