Question

Explain $PC{l}_5$ is possible but $NC{l}_5$ is not possible.

Answer 1

Nitrogen belongs to the second period so it has only s and p opticals in its valence shell.so N can show maximum covalency of 4 and that too it losses its lone pair of $e^{-s}$ so,n do not form Penta halides on the other hand ,P belongs to period 3 and has vacant D orbitals so it can exhibit covalency of 5 or 6 ,it can from pertahallides.