Question

Compare dipolement of nh3 molecule with that of nf3 molecule

Answer 1

Just looking at NH3 and NF3, you might assume that NF3 will have high dipole moment than NH3 as 'F' is more electronegative. But, NH3 has more dipole moment than NF3.

In NH3, N is more electronegative than H. So, N pulls the electrons from H towards itself and so, the direction of moment due to the N-H bonds is in the same direction as that of the lone pair of electrons on Nitrogen.

In NF3, F is more electronegative than N. So, all F atoms pull the electrons towards themselves. And, this resultant moment is opposite to the directions of that of the lone pair of electrons on the 'N' atom. And, since Dipole Moment is a vector quantity, the net dipole decreases.

And, so we have NH3 whose dipole moment is much higher than that of NF3.