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
(HF)
MO Diagram for O2
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