Compare dipole moment of NH₃ molecule with that of NF₃ molecule.

*NH₃ and NF₃ have pyramidal shape with lone pair of electrons on “N” atom
* In NH₃ the orbital dipole moment due to lone pair is in the same direction as the resultant dipole moment due to 3 N – H bonds
* In NF₃ orbital dipole moment due to lone pair is in opposite direction to the resultant dipole moment due to 3N – F bonds. therefore dipole moment of NH₃ is greater than NF₃.