Question

Compare and justify the dipole moment of ${NH}_3$ and ${NF}_3.$

Answer 1

The net dipole moment of $N{F}_3$ is less than that of $N{H}_3$.

In both molecules i.e., $N{H}_3$ and $N{F}_3$, the central atom $\left(N\right)$ has a lone pair electron and there are three bond pairs. Hence, both molecules have a pyramidal shape.

Since fluorine is more electronegative than hydrogen, it is expected that the net dipole moment of $N{F}_3$ is greater than $N{H}_3$. However, the net dipole moment of $N{H}_3$ is greater than that of $N{F}_3$.

In case of $N{F}_3$, fluorine is more electronegative than nitrogen, so it will attract the shared pair of electron towards itself from nitrogen. As a result dipole due to all $F$ is in opposite direction to the resultant dipole due to $N-F$ bonds, therefore the net dipole decreases.

In $N{H}_3$, Nitrogen is more electronegative than $H$, so it will attract the shared pair of electrons towards itself. As a result dipole due to Nitrogen is in same direction as the resultant dipole moment due to $N-H$ bond and hence the net dipole increases.

Hence, the net dipole moment of $N{F}_3$ is less than that of $N{H}_3$.