Question

What is the geometry of nitrogen atom in $NH _3, N \left( CH _3\right)_3$ and $N \left[ Si \left( CH _3\right)_3\right]_3$ ?
I. Trigonal planar
II. Trigonal pyramidal
III. Square planar

• A. I, I, I
• B. II, II, III
• C. II, I, II
• D. II, II, I

Answer 1

Answer: (D)

$NH _3$ Trigonal pyramidal due to
$N \left( CH _3\right)_3$ $i p-b p$ repulsion (instead of tetrahedral
In $N \left[\left( Si \left( CH _3\right)_3\right)_3\right]_3$ structure is triangular planar as lone pair on $N$-atom is transferred to the empty $d$-orbitals of silicon ( $p \pi-d \pi$ overlapping and its Lewis base character is lost. Thus, II, II, I