Question
Which of the following molecular species has unpaired electron(s) ?
A.
$${N_2}$$
B.
$${F_2}$$
C.
$$O_2^ - $$
D.
$$O_2^{2 - }$$
Answer :
$$O_2^ - $$
Solution :
$${N_2}\left( {7 + 7 = 14} \right);\sigma 1{s^2},\sigma {1^*}{s^2},\sigma 2{s^2},{\sigma ^*}2{s^2},$$ $$\left\{ {_{{\pi ^*}2p_z^2}^{{\pi ^*}2p_y^2},\,\,\sigma 2p_x^2} \right.$$
$${F_2}\left( {9 + 9 = 18} \right);\sigma 1{s^2},\sigma {1^*}{s^2},\sigma 2{s^2},{\sigma ^*}2{s^2},\sigma 2p_x^2,$$ $$\left\{ {_{\pi 2p_z^2}^{\pi 2p_y^2},\left\{ {_{{\pi ^*}2p_z^2}^{{\pi ^*}2p_y^2}} \right.} \right.$$
$$O_2^ - \left( {8 + 8 + 1 = 17} \right);\sigma 1{s^2},{\sigma ^*}1{s^2},\sigma 2{s^2},{\sigma ^*}2{s^2},\sigma 2p_x^2,$$ $$\left\{ {_{\pi 2p_z^2}^{\pi 2p_y^2},\left\{ {_{{\pi ^*}2p_z^1}^{{\pi ^*}2p_y^2}} \right.} \right.$$
$$O_2^{2 - }\left( {8 + 8 + 2 = 18} \right);\sigma 1{s^2},{\sigma ^*}1{s^2},\sigma 2{s^2},{\sigma ^*}2{s^2},\sigma 2p_x^2,$$ $$\left\{ {_{\pi 2p_z^2}^{\pi 2p_y^2},\left\{ {_{{\pi ^*}2p_z^2}^{{\pi ^*}2p_y^2}} \right.} \right.$$
∴ $$O_2^ - $$ is the only species having unpaired electron.