Question

NH3 and NF3 are isostructural with one lone pair on N-atom, but dipole moment of NH3 is

greater than that of NF3. Explain. please help to solve this problem other wise my teacher beat me ​

Answer 1

In NH3, N is the most electronegative element while in NF3, F is the most electronegative element. But in both the molecules, a lone pair of electrons is present.

So,in addition to bond polarity and structure, the unshared pair of electrons also influence dipole moment values.

The dipole moment of NF3 is expected to be larger than NH3. But the actual value of D.M of NF3 is 0.23D while that of NH3 is 1.46D ( where D is Debye).

In,NH3 the nitrogen being more electronegative and so the N-H bond is pointing towards N. A lone pair of electrons is attached on one side only and hence its other end becomes the negative end of a dipole, the bonded end being positive. This contributes a moment called lone-pair moment.