Question

Which of the following statements is true regarding $N{F}_3$ and $N{H}_3$?

• A. The dipole moment of $N{F}_3$ is zero
• B. The dipole moment of $N{F}_3$ is less than $N{H}_3$
• C. The dipole moment of $N{F}_3$ is more than $N{H}_3$
• D. The dipole moment of $N{H}_3$ is zero

Answer 1

The correct option is B The dipole moment of $N{F}_3$ is less than $N{H}_3$

In $N{H}_3$ and $N{F}_3$, the central nitrogen has three $\sigma$ bonds and one lone pair. Hence, both are $s{p}^3$ hybridized and posses trigonal pyramidal shape. In $N{H}_3$ and $N{F}_3$, the dipole moment vectors do not cancel out each other. Hence, both the molecules are polar in nature. In $N{H}_3$, the dipole moment vector of the bond and the lone pairs are in the same direction. But in $N{F}_3$, the dipole moment vector of lone pairs and bond pairs are opposite in direction. So, the net dipole moment will be the substractive effect of the two. Hence, the dipole moment of $N{H}_3$ is larger than $N{F}_3$.