Question

Why is ${\mathrm{O}}_2$ paramagnetic?

Answer 1

Magnetic Nature

• A substance's electron configuration can be used to identify its magnetic properties.
• The substance is paramagnetic if its electrons are unpaired.
• The substance is diamagnetic if all of its electrons are paired.
• Examples of paramagnetic: aluminum $\left(\mathrm{Al}\right)$ and sodium $\left(\mathrm{Na}\right)$.
• Examples of diamagnetic: copper $\left(\mathrm{Cu}\right)$ and silver $\left(\mathrm{Ag}\right)$.

Magnetic property of ${\mathbf{O}}_{\mathbf{2}}$

• Oxygen $\left({\mathrm{O}}_2\right)$ is paramagnetic due to the presence of two unpaired electrons in its last molecular orbital.
• The Molecular orbital electronic configuration is as follows:

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

• Molecular orbital diagram: