Question

Pick out the incorrect statement.

• A. The geometry around 'N' atom in trimethylamine is pyramidal
• B. The geometry around N atom in trisilylamine is planar
• C. The nitrogen atom in trimethylamine is $s{p}^3$ -hybridized; whilst in trisilylamine it is $s{p}^2$ -hybridized
• D. Trisilylamine has donor properties; whilst trimethylamine has no donor properties

Answer 1

Answer: (D)

In trimethylamine, 'N' atom is $s{p}^3$ -hybridized.



Due to the presence of lone pair in $s{p}^3$ -hybrid orbital, the geometry of ${\left(C{H}_3\right)}_{3}N$ becomes pyramidal around nitrogen.



This lone pair of electrons can be donated to electron-deficient species, e.g., ${\left(C{H}_3\right)}_{3}N\to B{F}_3$. This lone pair cannot be transferred to carbon atom, because carbon atom has no d-orbital in its valence shell. In ${\left(Si{H}_3\right)}_{3}N,$ the ' $N^{\prime }$ atom is $s{p}^2$ -hybridized.



The orientation of three $s{p}^2$ -hybrid orbitals is plane-triangular, therefore, the geometry around 'N' becomes plane-triangular. Here the lone pair of electrons is transferred to vacant d-orbitals to each of three silicon atoms forming $p\pi -d\pi$ multiple bonds. Consequently, ${\left(Si{H}_3\right)}_{3}N$ has no donor properties. For example

${\left(Si{H}_3\right)}_{3}N+B{F}_3\to$ No reaction.