Question

Which one of the following species exhibits diamagnetic behaviour?

• A. $N_2^{-}$
• B. $O_2^{2-}$
• C. $O_2^{+}$
• D. $O_2$

Answer 1

Answer: (B)

$O_2^{2-}$

The electronic configuration of the $O_2^{-2}$ ion containing 18 electrons can be written as:

$1s^2\ast 1s^{2}2s^2\ast 2s^{2}2p{z}^{2}2p{x}^{2}2p{y}^2\ast 2p{x}^2\ast 2p{y}^2$

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

$1s^2\ast 1s^{2}2s^2\ast 2s^{2}2p{z}^{2}2p{x}^{2}2p{y}^2\ast 2p{x}^1\ast 2p{y}^1$

The electronic configuration of the $O_2^{+}$ containing 16 electrons can be written as:

$1s^2\ast 1s^{2}2s^2\ast 2s^{2}2p{z}^{2}2p{x}^{2}2p{y}^2\ast 2p{x}^1$

For $N_2^{-}$

$1s^2\ast 1s^{2}2s^2\ast 2s^{2}2p{x}^{2}2p{y}^{2}2p{z}^2\ast 2p{x}^1$

Clearly, $O_2^{2-}$ is diamagnetic with zero unpaired electrons.