Molecular Orbital Theory(MOT)

              Molecular Orbital Theory
   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.
                Forming a Covalent Bond
n Molecules can form bonds by sharing electron
n Two shared electrons form a single bond
n Atoms can share one, two or three pairs of electrons
n forming single, double and triple bonds
n Other types of bonds are formed by charged atoms (ionic) and metal atoms (metallic).
Atomic and Molecular Orbitals:
n Orbital Mixing.
n When atoms share electrons to form a bond, their atomic orbitals mix to form molecular bonds. In order for these orbitals to mix they must:
n Have similar energy levels.
n Overlap well.
n Be close together.

Important Point:
n Each line in the diagram represents an orbital.
n The molecular orbital volume encompasses the whole molecule.
n The electrons fill the molecular orbitals of molecules like electrons fill atomic orbitals in atoms.
n Electrons go into the lowest energy orbital available to form lowest potential energy for the molecule.
n The maximum number of electrons in each molecular orbital is two. (Pauli exclusion principle)
n One electron goes into orbitals of equal energy, with parallel spin, before they begin to pair up. (Hund's Rule.)
Some example of MOT:

                  Molecular Orbital Diagram (H2)

Molecular Orbital Diagram (HF)

                                 MO Diagram for O2