Both the molecules NH3 and NF3 have pyramidal shape with a lone pair of electron on nitrogen atom. Although fluorine is more electronegative than nitrogen, the resultant dipole moment of NH3 (4.90 × 10–30Cm) is greater than that of NF3 (0.8 × 10–30Cm). This is because, 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 because of lone pair decreases the effect of the resultant N F bond moment which results in low dipole moment of NF3 as represented below :