Q. The electronegativity difference between N and F is greater than that between N and H yet the dipole moment of NH₃ (1.5 D) is larger than that of NF₃ (0.2 D). This is because :
A) in NH₃ as well as in NF₃ the atomic dipole and bond dipole are in the same direction
B) in NH₃ the atomic dipole and bond dipole are in the same direction whereas in NF₃ these are in opposite directions
C) in NH₃ as well as NF₃ the atomic dipole and bond dipole are in opposite directions
D) in NH₃ the atomic dipole and bond dipole are in the opposite directions whereas in NF₃ these are in the same directions
Explanation
[Solution from source] In NH₃ the lone pair's orbital dipole points away from N, the same way as the N–H bond dipoles (towards N), so they add up to 1.5 D. In NF₃ the N–F bond dipoles point towards the F atoms, opposite to the lone-pair dipole, so they largely cancel, leaving only 0.2 D. Answer (2).
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.