Which of the following best describes a Lewis acid?

A Lewis acid is defined as a substance that can accept an electron pair to form a covalent bond. This definition is part of the Lewis theory of acids and bases, which expands on the traditional Brønsted-Lowry definition that focuses on proton donation and acceptance. In the context of Lewis acid-base chemistry, a Lewis acid acts as an electron pair acceptor, making it essential in various chemical reactions, especially those involving coordination complexes and electrophilic reactions.

For example, when a Lewis acid reacts with a Lewis base (which is an electron pair donor), they form a new bond by the Lewis acid accepting an electron pair. This interaction is key in many chemical processes, including catalysis and organic synthesis. Understanding this concept lays the foundation for exploring how substances interact at a molecular level based on electron configurations.

The other definitions do not accurately describe a Lewis acid, as they either pertain to different acid-base theories or mischaracterize the role of a Lewis acid in chemical reactions.