# Relative Energies between LGOs and 2s orbital of oxygen in H2O MO Diagram

In this MO diagram, we find that the LGOs of the two premixed H1s orbitals are significantly higher in energy than oxygen's 2s orbital. Although oxygen's $$Z_{eff}$$ is considerably higher, is it really enough to make it so that the 2s orbital of oxygen is lower than the in-phase combination of two 1s orbitals?

• One of those oxygen p orbitals should not remain at the same level. There is one which points to the middle between the two hydrogen atoms and which thus obviously forms a bonding interaction, much stronger than that of the 2s orbital. – Jan Oct 25 '19 at 4:58