Question

calculate the number of unpaired electrons in o2+ and o2 2- ions by drawing molecular orbital diagram

Answer 1

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Molecular Orbital Energy Level Diagram of H2

Electronic configuration of 1st hydrogen atom: 1s1

Electronic configuration of 2nd hydrogen atom: 1s1

After combining atomic orbital gives one bonding molecular orbital and one anti-bonding molecular orbital. So bonding molecular orbital contains 2 electrons and anti-bonding orbital remains vacant. 

Electronic configuration of H2 molecule will be: σ 1s2



Similarly we can draw, molecular orbital energy diagram for H2+ and H2-.

H2+ ion is formed by combination of hydrogen atom containing one electron and hydrogen ion having no electron. Therefore, this molecular ion has only one electron.

So electronic configuration of H2+ is σ 1s1.

Similarly electronic configuration of H2- is σ1s2 σ1s*1 

Molecular Orbital Energy Level Diagram of C2

Electronic configuration of 1st carbon atom: 1s2 2s2 2px1 2py1 2pz0 

Electronic configuration of 2nd carbon atom: 1s2 2s2 2px1 2py1 2pz0 

After combining atomic orbital 1s2 and 1s2from each carbon atom gives one bonding molecular orbital and one anti-bonding molecular orbital. So both bonding and anti-bonding molecular orbital contain 2 electrons each. But energy level diagram for this bonding is not shown here. Similarly 2s2 and 2s2 atomic orbitals from each carbon atom combine to give one bonding molecular orbital and one anti-bonding molecular orbital each containing 2 electrons. Now 2p orbital from each atom combine to give σ 2pz orbital containing 2 electrons. Here σ2pz orbital is little more stable than bonding ∏ 2px and ∏ 2py orbitals. Both ∏ 2px and ∏ 2py are degenerate orbitals. So filling of electrons take place according to Hund's rule.

Electronic configuration of C2 molecule is :σ 1s2 σ1s2 σ2s2 σ2s2 (σ2pz)2 (∏ 2px)1 ( ∏ 2py)1