Construction of Molecular Orbital Diagrams

M.O. Diagram

We can now put in the electrons. The oxygen atom has 6 valence electrons in the 2s and 2p orbitals, 2s22p4. Each hydrogen atom has one 1s electron, giving us a total of 8. Simply build them up from the bottom of the diagram.

This gives us four pairs of electrons, two pairs in O-H s-bonds and two lone pairs on oxygen.