\(\mathrm{NH}_3\) has higher dipole moment than \(\mathrm{NF}_3\). This is explained on the basis of the following two reasons.
(1) The dipole formed between the lone pair and \(\mathrm{N}\) atom has to be taken into consi-deration which is in the direction of the lone pair.
(2) \(\mathrm{F}\) is more electronegative than \(\mathrm{N}\), therefore direction of bond is from \(\mathrm{N}\) to \(\mathrm{F}\) whereas \(\mathrm{N}\) is more electronegative than \(\mathrm{H}\), the direction of the bond is from \(\mathrm{H}\) to \(\mathrm{N}\). Thus (see diag.) resultant moment of \(\mathrm{N}-\mathrm{H}\) bonds add up to the bond moment of lone pair, whereas that of \(3 \mathrm{~N}-\mathrm{F}\) bonds partly cancels the resultant moment of lone pair. Hence, the net dipole moment of \(\mathrm{NF}_3\) is less than that of \(\mathrm{NH}_3\).