Select incorrect order among the following compounds

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${NH}_{3} > {NF}_{3} : Bond angle$

${NH}_{3} > {NF}_{3} : Dipole moment$

${NH}_{3} < {NF}_{3} : % s-Character of lone pair$

${NH}_{3} > {NF}_{3} : Lewis base$

answer is A, B, D.

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Detailed Solution

Electronegativity of N is more than H, hence the resultant dipole moment of NH₃ is pointed in one direction.

Electronegativity of N is less than F. In N-F bond, the direction of the dipole moment direction is towards F whereas the dipole moment of lone pair of N atom is on the opposite direction. So, the resultant dipole moment becomes reduced due to opposite dipole direction of N-F bonds and lone pair of N atom. Hence, dipole moment of NH₃ is more than NF₃.

In addition, the longer N−F bond length makes the bond pair-bond pair distance greater in NF3, than in NH₃, so that the bond pair-bond pair repulsion in NF₃ is less that in NH₃.

The net effect is that the bond angles are reduced more in NF₃.

There are 3 F atoms in NF₃ attracts the lone pair of electrons in N and hence it becomes difficult for N to loose that pair of electrons, and therefore acts as a weak base. But in NH₃, hydrogen is less electronegative then fluorine, and has less tendency to attract shared pair of electrons

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