The electronegaivity difference between `N` and `F` is greater than that between ` N` and `H` yet the dipole moment of `NH_2` ( 1 .5 D) is larger than that of ` NF_3 ( 0. 2 D)`. This is because :

Options

A. in `NH_3` as well as in `NF_3` , the atomic dipole and bond dipole are in the same direction
B. in `NH_3`, the atomic dipole and bond dipole are in the same direction whereas in `NF_3` these are in opposite directions
C. in `NH_3` as well as `NF_3` , the atomic dipole and bond dipole are in opposite directions
D. in `NH_3` the atomic dipole and bond dipole are in the opposite directions whereas in `NF_3` these are in the same directions

Answer

B

Explanation

F is more electronegative than N, therefore direction of bond is from N to F whereas N is more electronegative than H, the direction of the bond is from H to N. Thus whereas resultant moment of N-H bonds adds up to the bond moment of lone pair , that of 3N-F bonds partly cancel the resultant moment of lone pair . Hence, the net dipole moment of `NF_3` is less than that of `NH_3`.