What defines a Lewis Acid?

A Lewis acid is defined as a substance that accepts an electron pair from another molecule or ion during a chemical reaction. This definition is part of the broader Lewis theory of acids and bases, which extends the concept beyond the traditional definitions that focus on hydrogen ion (H⁺) concentration.

In this context, a Lewis acid does not necessarily have to produce H⁺ in solution or form covalent bonds directly; it is primarily involved in the acceptance of electron pairs. This ability to accept electrons allows Lewis acids to react with Lewis bases, which are electron pair donors, to form complexes. Examples of common Lewis acids include metal cations, such as Al³⁺ or transition metal complexes, which can accept electron pairs due to their positive charge and empty orbitals.

Understanding this definition is fundamental in identifying how Lewis acids participate in various chemical reactions, especially in coordination chemistry and organic reactions, where the transfer of electron pairs is crucial for bonding and reactivity.