Why nh3 has more dipole moment …

Dipole moment of NH₃ is higher than NF₃ molecule. This is due to the fact that dipole moment is a vector quantity and hence resultant dipole moment in a molecule will depend upon the direction of dipole moments of individual bonds. Nitrogen has a lone pair of electrons and is more electronegative than hydrogen. So, in case of NH₃, the orbital moment due to the lone pair of electrons on nitrogen is in the direction of lone pair of electrons is in the same direction of the 3 N-H dipoles. Thus, the molecule has a net dipole moment and it is polar.

In NF₃, Florine being more electronegative than Nitrogen pulls the shared pair of electrons of the N-F bonds towards itself. Because of this, the orbital moment due to lone pair of electrons and the resultant dipole moment of 3 N-F bonds point in the opposite directions to that of lone pair of electrons. This lowers the dipole moment of NF₃.

In both molecules i.e., NH₃ and NF₃, the central atom (N) has a lone pair electron and there are three bond pairs. Hence, both molecules have a pyramidal shape. Since fluorine is more electronegative than hydrogen, it is expected that the net dipole moment of NF₃ is greater than NH₃. However, the net dipole moment of NH₃ (1.46 D) is greater than that of NF₃ (0.24 D).

Since in case of  NF₃ , fluorine is more electronegative than nitrogen, so it will attract the shared pair of electron towards itself from nitrogen. As a result dipole due to all F is in opposite direction to the resultant dipole due to N-F bonds,therefore the net dipole decreases.

In NH₃, Nitrogen is more electronegative than H, so it will attract the shared pair of electrons towards itself.As  a result dipole due to Nitrogen is in same direction as the resultant dipole moment due to N-H bond& hence the net dipole increases.

Hence, the net dipole moment of NF₃ is less than that of NH₃.