Question

Which out of ${\mathrm{NH}}_3$ and ${\mathrm{NF}}_3$ has a higher dipole moment and why?

Answer 1

Dipole moment

• “It can be defined as the product of the magnitude of the charge and the distance between the centers of positive and negative charge.”

Dipole moment of ${\mathrm{NH}}_3$ and ${\mathrm{NF}}_3$

• The structure of ${\mathrm{NH}}_3$ and ${\mathrm{NF}}_3$ is as follows:-

• . In case of ${\mathrm{NH}}_3$ the orbital dipole due to the lone pair is in the same direction as the resultant dipole moment of the $\mathrm{N}–\mathrm{H}$ bonds.
• But in the case of ${\mathrm{NF}}_3$, the orbital dipole is in the direction opposite to the resultant dipole moment of the three $\mathrm{N}–\mathrm{F}$ bonds.
• The orbital dipole because of the lone pair decreases the effect of the resultant $\mathrm{N}–\mathrm{F}$ bond moments, which results in the low dipole moment of ${\mathrm{NF}}_3$.

Hence, the dipole moment of ${\mathrm{NH}}_3$ is higher compared to ${\mathrm{NF}}_3$.