Answer to Question #84524 in Inorganic Chemistry for anuj kumar

Question

Compare the electronic structure of N atom in trimethylamine and trisilylamine

Answer 1

1. (CH₃)₃N

Number of valence electrons 7(N) + 4(C)*3 = 19

Lewis structure is:

According to VSEPR theory there is 3 bounding pairs and one lone pair around the central atom, molecular structure is AX₃E - trigonal pyramidal. Hybridization of N atom is sp³.

2. (SiH₃)₃N

Number of valence electrons 7(N) + 4(C)*3 = 19

Lewis structure is:

According to VSEPR theory there is 3 bounding pairs and one lone pair around the central atom, we should expect the molecular structure to be AX₃E - trigonal pyramidal and Hybridization of N atom to be is sp³. But experimental data show that molecular structure of trisilylamine trigonal planar and hybridisation of N atom sp².

Explanation: in case of trimethylamine the lone pair of nitrogen is localised, hybridization on N is sp³ and molecular structure is trigonal pyramidal. But in trisilylamine antom of nitrogen has three bonds with atoms of Si, which have vacant d- orbitals. These d- orbitals and lone pair of nitrogen form additional bond: π-backbonding. The lone pair of nitrogen is delocalised and nitrogen is sp² hybridizad and the structure becomes trigonal planar.