Question

Why does ${\mathrm{BF}}_3$ act as a Lewis acid ?

Answer 1

Lewis Acid:

• Chemical compounds known as Lewis Acids contain vacant orbitals and can take electron pairs from Lewis Bases.
• This phrase was historically used to refer to chemical species that had an empty $\mathrm{p}-\mathrm{orbital}$ and a trigonal planar structure.
• Lewis acids are the compounds which are electron deficient(less than $8$ electrons in the central metal atom) and can accept the lone pair of electrons.

Reason behind ${\mathrm{BF}}_3$ acting as a Lewis Acid:

• ${\mathrm{BF}}_3$ has $6$ electrons in the central metal atom, boron. That's why, it is electron deficient and hence is a Lewis acid.