Molecular Orbital Theory?

Question

Would someone explain to me the Molecular Orbital Theory and how I could use it find to the bond order of a molecule?

Answer 1

If you draw out a molecular orbital digram, you will get a sense of how many valence electrons are in a bonding orbital versus how many are in an antibonding orbital.
Therefore, bond order can be described through the following equation:

(#bonding electrons-#antibonding electrons)/2

Answer 2

In "regular" orbital theory you figure out how the electrons are arranged for each individual atom and then have the "bonding" orbitals overlap to form bonds. The orbitals still belong to each individual atom; they just "share space" in the area of overlap.

In Molecular Orbital Theory, the electrons don't belong to the individual atoms, they belong to the whole molecule. When the atomic orbitals come together they create a new set of orbitals called molecular orbitals. You get a bonding orbital and an antibonding orbital. In the formation of the molecule there are spaces where the electrons will be attracted (bonding orbitals) and spaces where they will be repelled (antibonding orbitals). How well the atoms bond in the molecule depends on the balance between bonding and antibonding orbitals (called bond order). The bigger the bond order, the stronger the bond.

To determine bond order you first put all the electrons in their bonding and antibonding orbitals (your text should show you this list of orbitals) and then use the formula:

bond order = (#electrons in bonding orbitals - #electrons in antibonding orbitals)/2

Answer 3

Wow, that's a big question.

Molecular orbital theory takes the orbitals of two atoms that are bonded to each other, and adds or substracts them to create new orbitals. These orbitals depend on the energy of the input atomic orbitals.

Atomic orbitals have names like s,p,d and f, or hybrids of these such as sp3 or d2sp3.
Molecular orbitals have names like sigma, pi, sigma-star and pi-star. Star means that an orbital is "anti-bonding", which is an esoteric mathematical construct related to subtracting two orbitals.
Anyway a molecular orbital diagram probably looks something like
pi* pi*
sigma*
sigma
pi pi

sigma*
sigma

After filling in the electrons from both atoms, count up all of the bonding and antibonding electrons.

Bond order = (bonding - antibonding)/2.

Answer 4

Molecular orbital theory is based upon following postulates
-A covalent bond is formed by the overlapping of atomic orbitals which form molecular orbital.
-Bonding electrons occupy molecular orbital not atomic orbital.
-An electron in a molecular orbital is polycentric because it is influenced by more than one nuclei.
-Formation of molecular orbital is based on the linear combination of atomic orbitals (LCAO).
There are two kinds of molecular orbitals:
1. BONDING MOLECULAR ORBITAL
2. ANTI-BONDING MOLECULAR ORBITAL

Answer 5

Great question. But since there's no question mark I refuse to answer it, because I'm an English geek. Oh yeah, and there's no question either. Because I'm a sarcastic English/Science geek.