Heteronuclear Diatomics of Second-Row Elements

The two atoms in the heteronuclear diatomics are not related by any symmetry operation, and so we can assign symmetry labels to the individual AOs and then match up symmetry-related sets in the MO diagram. The assignments are straightforward, taking the molecular axis as Z  

The relative electronegativities of the two atoms in the molecule will give one set of AOs a lower energy than the other. 

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