Question

Which of the following molecules has a linear shape?

• A. $C{O}_2$
• B. $N{O}_2^{-}$
• C. $S{O}_2$
• D. $Cl{O}_2^{-}$

Answer 1

The correct option is A $C{O}_2$

The molecules assume different geometry based on the number of bond pairs/lone pairs in the valence shell of the central atom. However, lone pairs are ignored in assigning the shape of the molecule.

Steric number on the central atom = number of $\sigma$ bond + number of lone pair.

The pi electrons are not involved in deciding the geometry of the molecule.

$\left(a\right)$ On $C$, the number of $\sigma$ bond pairs is 2 and number of lone pairs is 0. So, the steric number is 2 and the hybridisation is $sp$. Therefore, the shape is linear.

$\left(b\right)$ On $N$, the number of $\sigma$ bond pairs is 2 and number of lone pairs is 1. So, the steric number is 3 and the hybridisation is $s{p}^2$. Therefore, the geometry is trigonal planar and the shape is bent.
$\left(c\right)$ On $S$, the number of $\sigma$ bond pairs is 2 and number of lone pairs is 1. So, the steric number is 3 and the hybridisation is $s{p}^2$. Therefore, the geometry is trigonal planar and the shape is bent.
$\left(d\right)$ On $Cl$, the number of $\sigma$ bond pairs is 2 and number of lone pairs is 2. So, the steric number is 4 and the hybridisation is $s{p}^3$. Therefore, the geometry is tetrahedral and the shape is bent.



Thus, $C{O}_2$ is Linear in shape.