Question

Among the following molecules / ions, $C_2^{2-},N_2^{2-},O_2^{2-},O_2$ which one is diamagnetic and has the shortest bond length?

• A. $C_2^{2-}$
• B. $N_2^{2-}$
• C. $O_2$
• D. $O_2^{2-}$

Answer 1

Answer: (A)

$C_2^{2-}{}^{-\sigma }1s^{2\sigma \ast }1s^{2\sigma }2s^{2\sigma \ast }2s^2{\left[{}^{\pi }2p_x^2\right]}^{\sigma }2p^2$
$B.O=\frac{10-4}{2}=3($ diamagnetic $)$
$N_2^{2--\sigma }1s^{2\sigma \ast }1s^{2\sigma \ast }2s^{2\sigma }2s^2\left[\pi 2p_x^2={}^{\pi }2p_y^2\right]\left[{}^{\pi }2p_x^1={}^{\pi \ast }2p_y^1\right]$
$B.O=\frac{10-6}{2}2($ paramagnetic $)$
$O_2^{2-}-\sigma 1s^{2\sigma }1s^{2\sigma }2s^{2\sigma }2s^{2\sigma }2p_z^2\left[{}^{\pi }2p_x^2={}^{\pi }2p_y^2\right]\left[{}^{\pi }2p_x^2={}^{\pi \ast }2p_y^2\right]$
$B.O=\frac{10-8}{2}=1($ diamagnetic $)$
$O_2^{-\sigma }1s^{2\sigma \ast }1s^{2\sigma }2s^{2\sigma \ast }2s^{2\sigma }2p_z^2\left[{}^{\pi }2p_x^2={}^{\pi }2p_y^2\right]\left[{}^{\pi }2p_x^1={}^{\pi \ast }2p_y^1\right]$
$B.O=\frac{10-6}{2}2($ paramagnetic $)$