Consider the following list of small molecules and ions: C₂ O₂^–, CN^–, O₂. CO, NO, NO⁺, C₂², OF^–. Identify

(a) all species that have a bond order of 3

(b) all species that are paramagnetic

(c) species that have a fractional bond order

Interpretation:

All the species which have a bond order of 3 should be identified from the given list of molecules. 

Concept Introduction:

Molecular orbital (MO) theory:  is a method for determining molecular structure in which electrons are not assigned to individual bonds between atoms, but are treated as moving under the influence of the nuclei in the whole molecule.

Bond order: It is the measure of number of electron pairs shared between two atoms.

Bond order = 12(Number of electrons in bondoing MOs-Number of electrons in antibonding MOs)

The list of given molecules and their electronic configuration in MO term and bond order are given below,

MoleculeNo. of electronsElectron  configurationBond order= 12(Nb−Na)C212(σ1s)2(σ*1s)2(σ2s)2(σ*2s)2( π2p)48−42 = 1O2−17(σ1s)2(σ*1s)2(σ2s)2(σ*2s)2 (σ2p)2( π2p)4( π*2p)3 10−72=1.5CN−14(σ1s)2(σ*1s)2(σ2s)2(σ*2s)2( π2p)4 (σ2p)2 10−42=3O216(σ1s)2(σ*1s)2(σ2s)2(σ*2s)2 (σ2p)2( π2p)4( π*2p)2 10−62=2CO14(σ1s)2(σ*1s)2(σ2s)2(σ*2s)2( π2p)4 (σ2p)2 10−42=3NO15(σ1s)2(σ*1s)2(σ2s)2(σ*2s)2 (σ2p)2( π2p)4( π*2p)110−52=2

Interpretation:

All the species which are paramagnetic should be identified from the given list of molecules. 

Concept Introduction:

Molecular orbital (MO) theory:  is a method for determining molecular structure in which electrons are not assigned to individual bonds between atoms, but are treated as moving under the influence of the nuclei in the whole molecule.

Bond order: It is the measure of number of electron pairs shared between two atoms.

Bond order = 12(Number of electrons in bondoing MOs-Number of electrons in antibonding MOs)

Atoms with unpaired electrons are called Paramagnetic. Paramagnetic atoms are attracted to a magnet.

Atoms with paired electrons are called diamagnetic. Diamagnetic atoms are repelled by  a magnet

Interpretation:

All the species which have fractional bond order should be identified from the given list of molecules. 

Concept Introduction:

Molecular orbital (MO) theory:  is a method for determining molecular structure in which electrons are not assigned to individual bonds between atoms, but are treated as moving under the influence of the nuclei in the whole molecule.

Bond order: It is the measure of number of electron pairs shared between two atoms.

Bond order = 12(Number of electrons in bondoing MOs-Number of electrons in antibonding MOs)