Question

Which molecule/ion out of the following does not contain unpaired electrons?

Options

• \[\ce{N^{+}2}\]

• \[\ce{O2}\]

• \[\ce{O^{2-}2}\]

• \[\ce{B2}\]

Answer 1

\[\ce{O^{2-}2}\]

Explanation:

The electronic configurations of the given molecules/ions are:

(i) \[\ce{N^{+}2}\] has 13 electrons in its structure and its molecular electronic configuration is: 

\[\ce{σ1s^2, σ^∗ 1s^2, σ 2s^2,σ^∗ 2s^2, σ 2p_x^2 = π 2p_y^2, π 2p_z^1}\].

Hence the ion of \[\ce{N^{+}2}\] has one unpaired electron in \[\ce{π 2p_z^1}\] sub-shell.

(ii) \[\ce{O2}\] has 16 electron in its structure and its molecular electronic configuration is: 

\[\ce{σ1s^2, σ^∗ 1s^2, σ 2s^2,σ^∗ 2s^2, σ 2p_x^2 = π 2p_y^2, π 2p_z^2}\].

\[\ce{= π^∗ 2p_x^1, π^∗ 2p_y^1}\]

Hence, the molecule of \[\ce{O2}\] has two unpaired electrons in its structure. 

(iii) \[\ce{O^{2-}2}\] has 18 electrons in its structure and its molecular electronic configuration is: 

\[\ce{σ1s^2, σ^∗ 1s^2, σ 2s^2,σ^∗ 2s^2, σ 2p_x^2 = π 2p_y^2, π 2p_z^2}\].

\[\ce{= π^∗ 2p_x^2, π^∗ 2p_y^2}\]

Hence, the peroxide ion \[\ce{O^{2-}2}\] does not contain any unpaired electrons.

(iv) \[\ce{B2}\] has 10 electrons in its structure and its electronic configuration is:

\[\ce{σ1s^2, σ^∗ 1s^2, σ 2s^2,σ^∗ 2s^2 = π 2p_y^1, π 2p_z^1}\].

Hence the structure of boron has two unpaired electrons.