 In heteronuclear diatomic molecules, mixing of atomic orbitals only occurs when the electronegativity values are similar.In carbon monoxide (CO, isoelectronic with dinitrogen) the oxygen 2s orbital is much lower in energy than the carbon 2s orbital and therefore the degree of mixing is low.The electron configuration 1σ21σ*22σ22σ*21π43σ2 is identical to that of nitrogen.