Both `NH_(3) and NF_(3)` have identical shapes and same state of hybridisation. Both N-H and N-F bonds have almost the same electronegativity difference. But still, the two molecules have different dipole moment values. How will you account for it ?

Explanation

Both `NH_(3)` and `NF_(3)` have pyramidal geometries and the electronegativity difference of bonding atoms in both `NH_(3)` (3.0-2.1=0.9) and `NF_(3)` (4.0-3.0=1.0) mlecules are also nearly the same. But the dipole moment of `NH_(3)` (1.46D) is more than that of `NF_(3)` (0.24D). This is explained on the basis of the difference in the directions of the dipole moments. In `NH_(3)` the dipole moment pair. But in `NF_(3),` the dipole moments of the three N-F bonds are in the direction opposite to that of the lone pair. Therefore, the resultant dipole moment in `NH_(3)` is more than in `NF_(3).`