Question

Why NH₃ has high dipole moment than NF₃ though both are pyramidal?

Answer 1

In case of NH₃ the orbital dipole due to lone pair is in the same direction as the resultant dipole moment of the N-H bonds, whereas in NF₃ the orbital dipole is in the direction opposite to the resultant dipole moment of the three N-F bonds. The orbital dipole become of lone pair decreases, which results in the low dipole moment.