Homonuclear diatomic molecules molecular orbital calculations

The molecular orbital energy-level diagrams of heteronuclear diatomic molecules are much harder to predict qualitatitvely and we have to calculate each one explicitly because the atomic orbitals contribute differently to each one. Figure 3.35 shows the calculated scheme typically found for CO and NO. We can use this diagram to state the electron configuration by using the same procedure as for homonuclear diatomic molecules. 

O and F) and can be treated separately, the order shown in Fig. 10.30 applies. When the 2s and 2p atomic orbitals have similar energies (on the left of Period 2, as far as N) and must be treated collectively, the order of molecular orbitals is more like that in Fig. 10.31. The change in order can be seen in Fig. 10.32, which shows the calculated energy levels for the Period 2 homonuclear diatomic molecules. In summary ... 

Heteronuclear diatomic molecules are not as symmetrical as homonuclear molecules, and we cannot evaluate coefficients in LCAO molecular orbitals by requiring that the orbitals have the proper symmetry. Variational, SCF, or density functional calculations must be used to evaluate the coefficients. 

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