Question

Which out of $N{H}_3$ and $N{F}_3$ has higher dipole moment and why?

Answer 1

The dipole moment of ammonia $\left(1.47D\right)$ is higher than the dipole moment of $N{F}_3$ $\left(0.24D\right)$. The molecular geometry is pyramidal for both the molecules. In each molecule, N atom has one lone pair. F is more electronegative than H and $N-F$ bond is more polar than $N-H$ bond. Hence, $N{F}_3$ is expected to have much larger dipole moment than $N{H}_3$. However reverse is true as in case of ammonia, the direction of the lone pair dipole moment and the bond pair dipole moment is same whereas in case of $N{F}_3$ it is opposite. Thus, in ammonia molecule, individual dipole moment vectors add whereas in $N{F}_3$, they cancel each other.