Question

Is HCl a Lewis Acid?

Answer 1

Lewis acids are the species or elements or compounds that accept an electron pair and have empty orbitals present in them which can accommodate the donated pair of electrons. A Lewis Base is the species that donates the electron pairs.

Complete answer:
Lewis acids are the species which have empty orbitals present in them and are capable of accepting electron pairs from Lewis Bases. The term, ‘Lewis Acids’ was used to describe the species which have a trigonal planar structure and have empty p-orbital. For example, consider the compound $B{R_3}$ (where R is a substituent that can be halide or any organic substituent). Other common examples of Lewis Acids include ${H^ + }ion,{H_3}{O^ + }ion$ , some metals cations like $M{g^ + },L{i^ + },F{e^{ + 3}}$ . Other than these any electron deficient $\pi - system$ can be considered as a Lewis Acid.
A Lewis base is a species that donates electron pairs to a Lewis acid. In a neutralisation reaction a covalent bond is formed between electron rich species (Lewis base) and electron deficient species (Lewis Acid). For this reason Lewis Bases are referred to as Nucleophiles and Lewis acids as electrophiles.
As we said earlier ${H^ + }$ is a common Lewis Acid, because it has no electrons present in it, can accept electrons, hence can act as a Lewis acid. Hence, we can say that ${H^ + }$ is a Lewis Acid, not HCl. Often the Lewis acids are referred to as electron loving or electrophiles and Lewis bases are known as nucleus loving or nucleophiles.

Note:
Remember that some compounds like water, $S{O_2}$ , and some other compounds act as both Lewis acids and base, since they can accept as well as donate the electron pairs based on the reaction.