Bonding and Antibonding Orbitals

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Can someone explain what an antibonding orbital is? Also, how do you fill the electrons? How are you supposed to figure out the # of antibonding and bonding electrons? How do you know if an atom will fill the antibonding or bonding orbital? Or does it fill both? If so why? I have read the book several times so please don't just refer me there. I find the book VERY confusing.

-- Anonymous, May 02, 2000

hey liz, wuz up baby? you want to know about bonding? well i know all about it. bonding is a simple process were things bind, therefore anitbonding is like when it unbinds. i learned this technique back in '52 during the cold war. it was a cold, cold, winter. me and my best friend sergi were out on the war front. the only thing we could do was play with the nuclear weapons and drink vodka and eat sausages. one time at war camp, my other friend olga ivankimoniwannalaya, she got a little freaky with her rifle and sausages. to cut this story short, she ended up dead, the moral of the story...who cares about this orbital rubbish.

-- Anonymous, May 02, 2000

Bonding orbitals are lower in energy than antibonding orbitals, therefor the bonding orbitals will fill up with electrons first. As to how they fill, refer to the Pauli exclusion principle which states that only two electrons can occupy a molecular orbital, and then only if they have opposite spins. Two molecular orbitals can be formed from two atomic orbitals. The molecular orbitals are obtained from linear combinations of atomic orbitals (either addition of the atomic orbitals or subtraction of the atomic orbitals--either adding or subtracting the wave functions of the atomic orbitals.) When you add the overlap between the two atomic orbitals, you build up electron density between the nuclei--this is a stable condition with an energy lower than that of the seperate atomic nuclei. This is the bonding MO. The antibonding MO is the result of the subtraction of the two atomic orbitals. The electron density is decreased, and the resulting orbital is higher in energy than the atomic orbitals. Now to understand how to fill the orbitals, we have to know the order of increasing energies of the orbitals--because electrons fill the orbitals according to the increasing energy just as in atoms. Let's take H2 for example: the 1s orbitals on 2 hydrogen atoms should give a sigma bonding molecular orbital and a sigma antibonding molecular orbital. the average energy of the two new orbitals must equal the average energy of the atomic s orbitals from which they were formed. (remember that the antibonding orbital is higher in energy and the bonding orbital is lower in energy so when we say the two energies here are equal we do mean the average!) Now just as in the atom, we fill the lower energy orbitals first...so the two electrons (one from each H) must go into the lower energy BONDING orbital. When the number of electrons in bonding orbitals exceeds the number of electrons in the antibonding orbitals, the molecule is lower in energy than the separate atoms. It is therefor easy to explain why when two atoms are left alone they spontaneously combine--lower energy is more stable. If the number of antibonding e-'s is greater this says that the species is unstable and should not exist.

As for the book, if one book doesn't explain to your satisfaction the concept you are trying to learn--try looking in another book. I am not trying to dissuade you from asking help here, far from it, just offering advice that will see you through some rough times in your college career and really life in general. :o)

I hope this helps, if not PLEASE email me!! t

-- Anonymous, May 02, 2000

I think vladimir hubichurcokoff could do a much better job of teaching this course. That says a lot.

-- Anonymous, May 03, 2000