Question

Which of the following has a higher dipole moment?

• A. NH$_3$
• B. NF$_3$
• C. Both have equal dipole moments
• D. None of the above

Hint:

Even though fluorine is more electronegative than hydrogen, molecular geometry and vector cancellation determine the net dipole moment.

Answer 1

The Correct Option is A

• NH$_3$ has a trigonal pyramidal shape with a lone pair on nitrogen. The dipole moment of the three N–H bonds and the lone pair add constructively.
• NF$_3$ also has a trigonal pyramidal shape, but the highly electronegative F atoms pull electron density away from N, opposing the dipole due to the lone pair.
• As a result, NH$_3$ has a higher net dipole moment than NF$_3$.