Question

The bond order and magnetic behaviour of $O_2^{-}$ ion are, respectively:

• A. 1.5 and diamagnetic
• B. 1.5 and paramagnetic
• C. 1 and paramagnetic
• D. 2 and diamagnetic

Answer 1

The correct option is B 1.5 and paramagnetic

According to MOT the electronic configuration of $O_2^{-}$ is:


$\sigma 1s^2,{\sigma }^{\ast }1s^2,\sigma 2s^2,{\sigma }^{\ast }2s^2,\sigma 2p_z^2,\pi 2p_x^2=\pi 2p_y^2,{\pi }^{\ast }2p_x^2={\pi }^{\ast }2p_y^1$
Bond order $=\frac{1}{2}$(Bonding electrons - anti bonding electrons)
Bond order $=\frac{1}{2}(10-7)=1.5$

Due to presence of unpaired electron it is paramagnetic.