Why N2 is more stable than O2. Explain on the basis of Molecular Orbital Theory

Molecular orbitals of nitrogen and oxygen is as below:
 
Nitrogen molecule has 14 electrons. So the electron distributions in molecular orbital are as below
 
N2 = σ1s2 σ*1s2   σ2s2 σ*2s2  σ2px2   π(2py2 2pz2)    
 
Bond order = (No. of electrons in bonding orbitals - No. of electrons in bonding orbitals)/2
                    =(10-4)/2 = 3
 
Oxygen molecule has 16 electrons. So the electron distributions in molecular orbital are as below
 
O2 = σ1s2 σ*1s2   σ2s2 σ*2s2  σ2px2   π(2py2 2pz2)  π*(2py1 2pz1)
 
 Bond order= (10-6)/2 = 2
 
As bond order of nitrogen is more than that of oxygen, nitrogen is more stable than oxygen.

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According to Molecular orbital theory, N2 has 3 bond orders whereas O2 has 2. Higher the bond order, more will be the overlapping of atoms, thus more will be stability. So, N2 is more stable than O2.

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