Can some explain to me the molecular orbital model?

Question

Thank you

Answer 1

When you use atomic orbitals to describe a molecule the orbitals (s,p,d,f) belong to each element. Bonds are believed to form in the area where the orbitals overlap but the orbitals continue to belong to their respective atoms.

In molecular orbital theory the electrons of the atoms involved in the molecule become "community" property and occupy a set of orbitals that belong to the molecule, not each individual atom. Some of the orbitals are such that bonding is enhanced (i.e. bonding orbitals) and some of the orbitals are such that repulsion is enhanced (i.e. antibonding orbitals). Instead of writing an electron configuration for each atom in the bond, you add up all of the electrons involved and place this TOTAL number of electrons into the correct molecular orbital list. The rules for filling these orbitals are pretty much the same as for the atomic orbitals:

a. always start at the lowest energy level (Aufbau principle)
b. no more than 2 electrons per orbital (Pauli principle)
c. for equivalent orbitals, distribute electrons evenly in all orbitals before pairing them up (Hund's Rule).

From this list of orbitals for the molecule certain information can be gained: bond order, paramagnetism, bond length etc.

Answer 2

The goal of molecular orbital theory is to describe molecules in a similar way to how we describe atoms, that is, in terms of orbitals, orbital diagrams, and electron configurations.

* The molecular orbitals are filled in a way that yields the lowest potential energy for the molecule.
* The maximum number of electrons in each molecular orbital is two. (We follow the Pauli exclusion principle.)
* Orbitals of equal energy are half filled with parallel spin before they begin to pair up. (We follow Hund's Rule.)
* Molecular orbitals are formed from the overlap of atomic orbitals.
* Only atomic orbitals of about the same energy interact to a significant degree.
* When two atomic orbitals overlap, they interact in two extreme ways to form two molecular orbitals, a bonding molecular orbital and an antibonding molecular orbital.