Why is dipole moment of NH3 > dipole moment of NF3 ?
Overall dipole moment of the system is the vector sum of the dipole moments within the system. In the figure attached, if dipole moments within the system are along the arrows (the direction of dipole moment vectors has been taken from positive to negative) and are represented by (say), \(\vec p_1, \vec p_2, \vec p_3, \vec p_4\), then the overall dipole moment of the system \(\vec P=\vec p_1+\vec p_2+\vec p_3+\vec p_4\). In the case of NF3, the vector sum will be less as the vector sum of three lower vectors is opposed by the vector pointing up (the vector due to lone pair of electrons), whereas in the case of NH3, the vector sum of three lower vectors is supported by the vector pointing up.
NH3_NF3_Dipole_Moment.png
Sir, may I also know what is orbital dipole and also if it has connection with the answer?
In this context orbital dipole can mean the electric dipole due to the location of lone pair of electrons. But often orbital dipole may have reference to magnetism which may not fit in above context.