[CrimpJiggler]

I'm a visual thinker and one area of chemistry I've been struggling to learn for a long time is MO theory. The words confuse the hell outta me and the diagrams aren't sufficient for me to get a complete image of the whole thing in my head. I've seen diagrams like this:

which aren't bad at all (I could use images like this in my head if I knew exactly what they represented) but the problem is I don't know how these pictures work as a whole. For example I fill the bonding orbital and I have that cigar shaped MO. What happens when I filled the antibonding orbital? Does it cancel out the whole bonding orbital or something? In other words, does the bonding orbital disappear when the antibonding orbital gets filled and then whats left are those 2 pieces of the antibonding MO? Heres a better diagram:

looking at this, I think I'm on the verge of gaining an understanding but I don't know how all these parts combine together as a whole. Look at the 2 MOs at the bottom. The antibonding orbital isn't actually located above the bonding one is it? Is this diagram actually representing the spacial positioning of the MOs or is this an abstract representation of their energy levels? Are all these individual MOs actually present in ethane or do the lower ones get canceled out so all thats left are the LUMO and HOMO?

[Borek]

All orbitals occupy the same space, they overlap. They are drawn separately, but that's just a convention.

On the first picture there are black dots - these are nuclei, and you should reposition the drawings so that nuclei are in the same place. Same with the second picture, you just have something similar to skeleton model in the centers.

Where orbitals overlap overall electron density is a sum of the densities from each of the orbitals.

[CrimpJiggler]

Thanks Borek. I read somewhere that antibonding electrons cancel out the bonding electrons. When you fill an antibonding s orbital, do the electrons of the bonding s orbital become confined to that area of space between the 2 lobes of the antibonding orbital?

[Borek]

Thanks Borek. I read somewhere that antibonding electrons cancel out the bonding electrons. When you fill an antibonding s orbital, do the electrons of the bonding s orbital become confined to that area of space between the 2 lobes of the antibonding orbital?

Shapes of orbitals don't change, what changes is the energy. It is bonding energy of electrons on the bonding orbital that is canceled by the energy of electrons on antibonding orbital.

[CrimpJiggler]

When 2 atoms bond together, do all their atomic orbitals combine? For example when K bonds to Br, do their 1s, 2s, 2p etc. orbitals combine together to form molecular orbitals? This seems to be what every explanation I've read state, I'm just asking to verify this because I have a very hard time accepting this. What about a triatomic molecule like NO2, do the atomic orbitals of all 3 atoms combine to form triple molecular orbitals?