Question

Compare the stabilities of O₂ , O₂^-,O₂^2-

Answer 1

The stabilities of these can be best explained using Molecular orbital theory.
 
(i)  Formation Oxygen molecule:
Electronic configuration of oxygen atom-1s² 2s² 2p⁴
Atomic orbitals of oxygen combine to form molecular orbitals.
BO = bonding orbitals 
ABO = Anti-bonding orbitals
 O₂:
   

Electronic configuration of Oxygen molecule = 



Bond order in Oxygen molecule (O2)=
=½ [(Number of bonding electrons) – (number of anti-bonding electrons)]
= ½ [10 – 6]
= 2

O2- :

Bond order in Oxygen molecule (O2-)
=½ [(Number of bonding electrons) – (number of anti-bonding electrons)]
= ½ [10 – 7]
= 1½
 
O₂^2-:

Bond order in Oxygen molecule (O2-2)
=½ [(Number of bonding electrons) – (number of anti-bonding electrons)]
= ½ [10 – 8]
= 1
With the increase in number of electrons in anti-bonding orbital the stability and bond order of the molecule decreases.
Thus Decreasing order of stability is: O₂ > O₂^- > O₂^2-