Question

Explain why ${\mathrm{BF}}_3$ behaves as a lewis acid.

Answer 1

Lewis acids:

Lewis acids are those compounds that accept lone pairs of electrons from other elements to their octet.

Structure of ${\mathrm{BF}}_3$:

1. The electronic configuration of boron is $1{\mathrm{s}}^{2}2{\mathrm{s}}^{2}2{\mathrm{p}}^1$.
2. It has three electrons in its valence shell.
3. Hence it can form only three covalent bonds, which leads to only six electrons being present around the boron atom.
4. Boron forms three covalent bonds with three Fluorine atoms.

Acts as an acid:

1. In the case of ${\mathrm{BF}}_3$, Boron forms three covalent bonds with three Hydrogens but the octet of boron is still incomplete.
2. So, to complete the octet Boron accepts two lone electrons from other atoms of compounds.
3. Hence, according to lewis acid-base theory, as Boron accepts lone pair of electrons, so it acts as a lewis acid.

Therefore, ${\mathrm{BF}}_3$ acts as a lewis acid