## Molecular Orbital Theory

Molecular Orbital Theory

•In
the molecular orbital model, orbitals on individual atoms interact to produce new orbitals, called molecular orbitals, which are now identified
with the whole molecule.

•THROW
OUT THE IDEA OF LOCALIZED BONDING

Why Do Atoms Form Molecules

The Aufbau principle tells us to put electrons into the lowest energy
configuration in atoms. Similarly,
molecules form when the

__total energy of the electrons is lower in the molecule than in individual atoms__.
Just as we did with quantum theory for electron in atoms,
we will use the molecular quantum theory to obtain.

1.
Molecular Orbitals What are the shapes of the waves?

Where are the lobes and nodes?

What is the electron density distribution?

2.
Allowed Energies. How do the allowed
energies change when bonds form?

**Wave-functions and Energies: Bonding in H2**

If we calculate the wave functions
and allowed energies of a two proton, two electron system as a function of
separation between the nuclei (the

__bond length__), then we see how two atoms are transformed into a molecule.
This calculation tells us

•Whether a bond forms -
Is the energy of the molecule lower than the two atoms?

•The equilibrium bond
length -
What distance between the nuclei corresponds to the minimum in the energy?

•The structure of the
bond -
What is the electron density (charge) distribution (y2)?

Electronic
properties of the molecules

Diatomic
Molecular Orbital Theory

•In the case of diatomic molecules, the
interactions are easy to

see and may be thought of as arising from the
constructive

interference of the electron waves (orbitals) on two different

atoms, producing a bonding
molecular orbital, and the

destructive interference of the electron waves,
producing an

antibonding molecular orbital

•This Approach is called LCAO-MO

(Linear
Combination
of Atomic
Orbitals
to Produce

**Also read ..**

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