Antibonding orbital, LUMO and HOMO

[lo2]

Hi there

I have some questions regarding those three things.

First off, the antibonding orbital, which I am having a hard time comprehending. So as far as I understand most atoms in organic chemistry have those antibonding orbitals, for instance a carbonyl carbon, where I imagne the antibonding orbital to point in the opposite direction of the double bond to the carbonyl or something, so is that so? And what about for instance methane where are its antibonding orbitals located?

I think I have got the fact that when another atom starts to put electrons into the antibonding orbital, it breaks down the real bond, and all of a sudden the antibonding orbital is now the bonding one. So is that true? And then how come not all atoms can put electrons in the antibonding orbital and thereby bind?

Also I have come across the terms LUMO (lowest unoccupied molecular orbital) and HOMO (highest unoccupied molecular orbital) and I really do not understand what it is, so could anyone please expalinthis?

BTW looks like a really cool forum! :)

 

[DrDu]

I would recommend you to read first the entry on wikipedia on "molecular orbital theory" and follow the links, the following one seems to be quite nice:


http://www.chm.davidson.edu/vce/MolecularOrbitals/index.html