I'm trying to understand how to draw MO diagram for molecules such as CO, HF, and NO. I am finding so much conflicting information on how to order the σ and pi boxes in the diagram. Now, I know that the more electronegative atom's orbitals are going to be lower in energy than the less electronegative atom. I have learned so far that there are two ways to set up MO diagrams for homo-nuclear diatomic molecules: one was with the pi 2p bonding MO below the σ2p bonding orbital and the reverse for atoms with an atomic number ≥8. How can this be applied to heteronuclear molecules? I keep finding different sources using both ways: [PLAIN]http://i60.tinypic.com/20tgz61.png[/PLAIN] [PLAIN]http://i62.tinypic.com/17bdwx.gif[/PLAIN] Are both correct then? Thanks!