Question

What is a Lewis acid?

Answer 1

Hint: The thermodynamic aspect that can help us determine how a Lewis adduct is formed is known as Lewis acid and basis. An adduct is formed by the direct addition of multiple molecules to the component. The terms Lewis acids and Lewis bases are used interchangeably with electrophile and nucleophile.

Complete answer:
The concept of Lewis acids and bases was given by Gilbert N. Lewis.
Now, a chemical species that can accept a pair of electrons from a Lewis base is known as a Lewis acid. A Lewis acid can accept electrons due to the presence of empty orbitals in it.
The Lewis base shares electrons with a Lewis acid to form a Lewis adduct.
Also, a dative bond is formed when electrons furnished by the Lewis base are shared between the Lewis acid and the Lewis base.
For example, trimethyl borane $Me{{B}_{3}}$ is a Lewis acid that accepts a lone pair of electrons from the Lewis base ammonia $N{{H}_{3}}$ to form a Lewis adduct. It can be represented as follows
\[M{{e}_{3}}B+:N{{H}_{3}}\to \]
\[M{{e}_{3}}B\leftarrow N{{H}_{3}}\text{ or }M{{e}_{3}}B:N{{H}_{3}}\text{ or }M{{e}_{3}}B\bullet N{{H}_{3}}\]
Now, typically, the term Lewis acid is limited to empty p orbitals containing trigonal planar molecules. But sometimes complexes like $AlC{{l}_{3}}$ are also considered to be Lewis acids. metal ions like $N{{a}^{+}}$ or $M{{g}^{2+}}$ form Lewis adducts by bonding with complex ligands.
A proton ${{H}^{+}}$ is said to be the most complicated yet strongest Lewis acid.

Note:
Compounds that can accept a pair of electrons as well as donate a pair of electrons behave as both Lewis acid and a Lewis base and can be called by either of the names depending on the reaction. For example, water molecule ${{H}_{2}}O$.