Question -
Answer -
In both molecules i.e., NH3┬аand NF3, the central atom (N) hasa lone pair electron and there are three bond pairs. Hence, both molecules havea pyramidal shape. Since fluorine is more electronegative than hydrogen, it isexpected that the net dipole moment of NF3┬аis greater than NH3. However, the net dipolemoment of NH3┬а(1.46 D) is greater than that of NF3┬а(0.24 D).
This can be explained on the basis of thedirections of the dipole moments of each individual bond in NF3┬аand NH3. These directions can beshown as:
Thus, the resultant momentof the NтАУH bonds add up to the bond moment of the lone pair (the two being inthe same direction), whereas that of the three N тАУ F bonds partly cancels themoment of the lone pair.
Hence,the net dipole moment of NF3┬аis less than that ofNH3.