Question

If Hund's rule is not applicable, then bond order and magnetic behavior of $O_2$ molecule is:

• A. $2$, Paramagnetic
• B. $2$, Diamagnetic
• C. $2.5$, Paramagnetic
• D. $2.5$, Diamagnetic

Answer 1

The correct option is B $2$, Diamagnetic

If Hund's rule is not obeyed, the oxygen molecule will have a bond order of 2 and it will be diamagnetic.

The electronic configuration of the $O_2$ containing 16 electrons can be written as:

$\left[\right(\sigma 1s{)}^2\left({\sigma }^{\ast }1s^2\right)\left(\sigma 2s{)}^2\right({\sigma }^{\ast }2s^2\left)\right(\sigma 2p_z{)}^2(\pi 2p_x^2=\pi 2p_y^2)({\pi }^{\ast }2p_x^1={\pi }^{\ast }2p_y^1)$]

This is because the two electrons present in antibonding pi 2p orbital will pair up and the bond order will remain unaffected.

So, bond Order = $\frac{6-2}{2}=2$