Question

The pairs of species of oxygen and their magnetic behaviours are noted below. Which of the following presents the correct description?
A.\[O,O_2^{2 - }\]- Both paramagnetic
B.\[O_2^ - ,O_2^{2 - }\]- Both diamagnetic
C.\[{O^ + },O_2^{2 - }\]- both paramagnetic
D.\[O_2^ + ,{O_2}\]- both paramagnetic

Answer 1

Hint: In paramagnetic species electrons are unpaired but in the diamagnetic species all electrons are paired up. It is known that there are eight electrons in an oxygen atom. To decide if electrons are paired or unpaired is concluded on the basis of filling up of orbitals.

Complete step by step answer:
Let us look at the molecular orbital configurations of these oxygen atom species:

\[
  {O_2}^ + = \sigma 1{s^2},{\sigma ^*}1{s^2},\sigma 2{s^2},{\sigma ^*}2{s^2},\sigma 2p_z^2,\pi 2p_x^2 \approx \pi 2p_y^2,{\pi ^*}2p_x^1 \approx {\pi ^*}2p_y^0 \\
  {O_2}^ - = \sigma 1{s^2},{\sigma ^*}1{s^2},\sigma 2{s^2},{\sigma ^*}2{s^2},\sigma 2p_z^2,\pi 2p_x^2 \approx \pi 2p_y^2,{\pi ^*}2p_x^1 \approx {\pi ^*}2p_y^1 \\
  {O_2}^{2 - } = \sigma 1{s^2},{\sigma ^*}1{s^2},\sigma 2{s^2},{\sigma ^*}2{s^2},\sigma 2p_z^2,\pi 2p_x^2 \approx \pi 2p_y^2,{\pi ^*}2p_x^1 \approx {\pi ^*}2p_y^2 \\
  {O_2} = \sigma 1{s^2},{\sigma ^*}1{s^2},\sigma 2{s^2},{\sigma ^*}2{s^2},\sigma 2p_z^2,\pi 2p_x^2 \approx \pi 2p_y^2,{\pi ^*}2p_x^1 \approx {\pi ^*}2p_y^1 \\
 \]

\[O = 1{s^2}2{s^2}2p_x^22p_y^12p_z^1\]

\[{O^ + } = 1{s^2}2{s^2}2p_x^12p_y^12p_z^1\]
 We can have a brief view of the magnetic behaviour of molecules. If all the molecular orbitals in a molecule are doubly occupied by the electrons, the substance is diamagnetic whereas if one or more molecular orbitals are singly occupied by electrons, it is paramagnetic.
 From these molecular orbital diagrams, we can see that O atoms and \[{O_2}\] molecules have two unpaired electrons so these are paramagnetic. \[{O_2}^ - \]and \[{O_2}^ + \] have one unpaired electron each and so both of them are paramagnetic. \[{O^ + }\] has three unpaired electrons so it is paramagnetic too. Whereas only \[{O_2}^{2 - }\] has no unpaired electrons and is diamagnetic.

Hence, the correct option is (D).

Note:

We can see that electronic configuration is discussed if we have one atom, like oxygen. But if we are given any molecule, then molecular orbitals are considered as in case of oxygen anion as a molecule has subshells, shells and orbitals.