Question

The pairs of species of oxygen and their magnetic behaviours are noted below. Which of the following presents the correct description?

• A. $O_2^{-},O_2^{2-}$ - Both diamagnetic
• B. $O^{+},O_2^{2-}$ - Both paramagnetic
• C. $O_2^{+},O_2$ - Both paramagnetic
• D. $O,O_2^{2-}$ - Both paramagnetic

Answer 1

The correct option is C $O_2^{+},O_2$ - Both paramagnetic

The molecular orbital configurations of $O_2^{+},O_2^{-},O_2^{2-}$ and $O_2$ are
$O_2^{+}=\sigma 1s^2,\stackrel{\ast }{\sigma }1s^2,\sigma 2s^2,\stackrel{\ast }{\sigma }2s^2,\sigma 2p_z^2,\pi 2p_x^2$
$\approx \pi 2p_y^2,\stackrel{\ast }{\pi }2p_x^1\approx \stackrel{\ast }{\pi }2p_y^0$
$O_2^{-}=\sigma 1s^2,\stackrel{\ast }{\sigma }1s^2,\sigma 2s^2,\stackrel{\ast }{\sigma }2s^2,\sigma 2p_z^2,\pi 2p_x^2$
$\approx \pi 2p_y^2,\stackrel{\ast }{\pi }2p_x^2\approx \stackrel{\ast }{\pi }2p_y^1$
$O_2^{2-}=\sigma 1s^2,\stackrel{\ast }{\sigma }1s^2,\sigma 2s^2,\stackrel{\ast }{\sigma }2s^2,\sigma 2p_z^2,\pi 2p_x^2$
$\approx \pi 2p_y^2,\stackrel{\ast }{\pi }2p_x^2\approx \stackrel{\ast }{\pi }2p_y^2$
$O_2=\sigma 1s^2,\stackrel{\ast }{\sigma }1s^2,\sigma 2s^2,\stackrel{\ast }{\sigma }2s^2,\sigma 2p_z^2,\pi 2p_x^2$
$\approx \pi 2p_y^2,\stackrel{\ast }{\pi }2p_x^1\approx \stackrel{\ast }{\pi }2p_y^1$
and the electronic configuration of $O$ and $O^{+}$ are
$O=1s^2,2s^2,2p_x^2,2p_y^1,2p_z^1$
$O^{+}=1s^2,2s^2,2p_x^1,2p_y^1,2p_z^1$
As $O_2^{+},O_2,O_2^{-},O$ and$O^{+}$ have unpair electrons, hence are paramagnetic.