why N(CH3)3 is pyramidal but N(SiH3)3 is planar while both C and Si belonging to same group and having same valence shell EC?
N(SiH3)3 has a planar geometry due to back bonding between empty 3d orbital of Si and filled 2p orbital of N.
(CH3)3N has pyramidal geometry due to absence of back bonding. Nitrogen is sp3 hybridized out of which 3 hybrid orbitals are used for bond making and 1 lone pair is present in fourth orbital.