Question

${PF}_5$ is known, whereas ${NF}_5$ is not. Explain.

Answer 1

Phosphorus has vacant $d$-orbitals in its valence shell and therefore, can extend its bonding beyond octet. Nitrogen does not have $d$-orbitals in its valence shell and therefore, cannot expand its valence shell beyond four. As a result, $N$ cannot form pentahalides such as ${NF}_5$