The electronegativity difference between N and $\mathrm{F}$ is greater than that between $\mathrm{N}$ and $\mathrm{H}$ yet the dipole moment of ${\mathrm{NH}}_3(1.5\mathrm{D})$ is larger than that of ${\mathrm{NF}}_3(0.2\mathrm{D})$. This is because.