Question

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

Answer 1

$N{H}_3$ and $N{F}_3$ both the molecules have pyramidal shape with a lone pair of electrons on nitrogen atom. Although fluorine is more electronegative than nitrogen, then resultant dipole moment of $N{H}_3(4.90\times {10}^{-30}Cm)$ is greater than that of $N{F}_3(0.8\times {10}^{-30}Cm)$. This is because, in case of $N{H}_3$ the orbital dipole due to lone pair is in the same direction as the resultant dipole moment of the $N-H$ bonds, whereas in $N{F}_3$ the orbitalk dipole is in the direction opposite to the resultant dipole moment of the three $N-F$ bond. The orbital dipole because of lone pair decreases the effect of the resultant $N-F$ bond moments, which results in the low dipole moment of $N{F}_3$ as represented in the figure.