Question

The electronegativity difference between $N$ and $F$ is greater than that between $N$ and $H,$ yet the dipole moment of $NH_{3} (1.5 D)$ is larger than that of $NF_{3} (0.2 D).$ This is because

• A. In $NH_{3}$ the atomic dipole and bond dipole are in the same direction, whereas in $NF_{3}$ these are in opposite directions
• B. In $NH_{3}$ as well as $NF_{3}$ the atomic dipole and bond dipole are in opposite directions
• C. In $NH_{3}$ the atomic dipole and bond dipole are in the opposite directions, whereas in $NF_{3}$ these are in the same direction
• D. In $NH_{3}$ as well as in $NF_{3}$ the atomic dipole and bond dipole are in the same direction

Answer 1

Answer: (A)

In $NH_{3}$ the atomic dipole and bond dipole are in the same direction, whereas in $NF_{3}$ these are in opposite directions so in the former case they are added up whereas in the latter case net result is the reduction of dipole moment. It has been shown in the following figure: