Trisilylamine, , is notably planar, whereas trimethylamine, , is pyramidal. This structural anomaly — Chemical Bonding Chemistry Question

💡 Solution & Explanation

In $N(SiH_3)_3$, the lone pair on Nitrogen back-donates into the empty 3d orbitals of Silicon ($p\pi-d\pi$ back bond). This delocalizes the lone pair, forcing Nitrogen to re-hybridize to $sp^2$ and creating a planar geometry. Carbon lacks d-orbitals, so $N(CH_3)_3$ remains $sp^3$ (pyramidal).