pBlock ElementsII 1 Question 1
1. The correct statement among the following is
(2019 Main, 12 April I)
(a) $\left(\mathrm{SiH}{3}\right){3} \mathrm{~N}$ is planar and less basic than $\left(\mathrm{CH}{3}\right){3} \mathrm{~N}$.
(b) $\left(\mathrm{SiH}{3}\right){3} \mathrm{~N}$ is pyramidal and more basic than $\left(\mathrm{CH}{3}\right){3} \mathrm{~N}$.
(c) $\left(\mathrm{SiH}{3}\right){3} \mathrm{~N}$ is pyramidal and less basic than $\left(\mathrm{CH}{3}\right){3} \mathrm{~N}$.
(d) $\left(\mathrm{SiH}{3}\right){3} \mathrm{~N}$ is planar and more basic than $\left(\mathrm{CH}{3}\right){3} \mathrm{~N}$.
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Solution:
- The correct statement is that $\left(\mathrm{SiH}{3}\right){3} \mathrm{~N}$ is planar and less basic than $\left(\mathrm{CH}{3}\right){3} \mathrm{~N}$. The compounds trimethylamine $\left(\mathrm{CH}{3}\right){3} \mathrm{~N}$ and trisilylamine $\left(\mathrm{SiH}{3}\right){3} \mathrm{~N}$ have similar formulae, but have totally different structures. In trimethylamine the arrangement of electrons is as follows :
In trisilylamine, three $s p^{2}$ orbitals are used for $\sigma$-bonding, giving a plane triangular structure.
