`(SiH_(3))` is a weaker base than `(CH_(3))_(3)`N. Explain.

Explanation

Trimethylamine `N(CH_(3))_(3)` involving C-N bonds is pyramidal wherease trisilicy lamine `N(SiH_(3))_(3)` which involves Si-N bonds is of planar nature. The structures of these compounds are shown in the figure given below :

In trimethylamine, the nitrogen atom is `sp^(3)` hybridised and the structure of the molecule is pyramidal similar to that of ammonia in which the three hybridised orbitals of nitrogen atom are involved in the axial overlap `(sigma`-bonds) with the orbitals of carbon atoms. The lone electron pair on nitrogen atom is free and the amine acts as a Lewis base. However, the structure of trisilicylamine has been found to be planar which means that the nitrogen atom is `sp^(2)` hybridised and is forming N-Si sigma bonds. The lone pair of electrons present on the nitrogen atom is involved in the sidewise overlap with the vacant 3d orbitals of silicon atoms and this is called `dpi-ppi` bonding as shown by dotted lines in the Figure. It is not esily available and as a result trisilicyl amine is a weaker base than trimethy lamine.