Bond Order: It is defined as 0.5 times the difference between the “No. of electrons present in bonding orbitals and No. of electrons present in anti-bonding orbitals” of a molecule.

Bond Order = 0.5(N_{b} – N_{a});

N_{a }: No. of anti-bonding electrons

N_{b }: No. of bonding electrons

O_{2} contain 16 electrons i.e. 8 electrons from each O- atom.

Electronic configuration of O_{2} is:

\( [\sigma – (1s)]^{2}[\sigma ^{*}(1s)]^{2}[\sigma (2s)]^{2}[\sigma ^{*}(2s)]^{2}\)

\( [\sigma (1p_{z})]^{2}[\pi (2p_{x})]^{2}[\pi (2p_{y})]^{2}[\pi^{*} \)

\( (2p_{x})]^{1}[\pi^{*} (2p_{y})]^{1}1As\; 1s\)

- orbital of each O- atom does not involve in the bonding,

No. of bonding electrons = N_{b} = 8

No. of anti-bonding electrons = N_{a} = 4

Now,

Bond order = 0.5(8 – 4) = 2

Electronic configuration of \( O_{2}^{-}\) (superoxide) is:

\( KK[\sigma(2s)]^{2}[\sigma ^{*}(2s)]^{2}[\sigma (2p_{z})]^{2}\)

\( [\pi (2p_{x})]^{2}[\pi (2p_{y})]^{2}[\pi^{*} (2p_{x})]^{2}[\pi^{*} (2p_{y})]^{1}\)

No. of bonding electrons = N_{b} = 8

No. of anti-bonding electrons = N_{a} = 5

Now,

Bond order = 0.5(8 – 5) = 1.5

Electronic configuration of \( O_{2}^{+}\) is:

\( KK[\sigma(2s)]^{2}[\sigma ^{*}(2s)]^{2}[\sigma (2p_{z})]^{2}\)

\( [\pi (2p_{x})]^{2}[\pi (2p_{y})]^{2}[\pi^{*} (2p_{x})]^{1}\)

No. of bonding electrons = N_{b} = 8

No. of anti-bonding electrons = N_{a} = 3

Now,

Bond order = 0.5(8 – 3) = 2.5

Electronic configuration of N_{2} is:

\( [\sigma(1s)]^{2}[\sigma ^{*}(1s)]^{2}[\sigma (2s)]^{2}[\sigma ^{*}(2s)]^{2}\)

\( [\pi (2p_{x})]^{2}[\pi (2p_{y})]^{2}[\pi (2p_{z})]^{2}\)

No. of bonding electrons = N_{b} = 10

No. of anti-bonding electrons = N_{a} = 4

Now,

Bond order = 0.5(10 – 4) = 3

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