6. Aslam0Alaikum to my respectable
teacher and my class fellows and
Today My presentation on topic
First off all, I want to tell you about
defination,procedure and structure of
MOT of some molecules .
7. In 1927 hietler and london proposed the valance
Bond theory .Valence Bond Theory fails to
answer certain questions like Why He2 molecule
does not exist and why O2 is paramagnetic?
Therefore in 1932 F. Hood and Robert S.
Mulliken came up with theory known
as Molecular Orbital Theory to explain
questions like above. According to Molecular
Orbital Theory individual atomic orbitals combine
to form molecular orbitals, as the electrons of an
atom are present in various atomic orbitals and
are associated with several nuclei.
8. MOT means molecular orbital theory
When two atoms are combine to form a
molecule then Each atoms of atomic orbital
combine to form molecular orbital, Molecular
orbitals are classified on the basis of energy,
1) Bonding Orbital
2) Anti Bonding Orbital
The orbital having lowest energy is called
The orbital having high energy is called
9. When addition of wave function takes
place, the type of molecular orbitals formed
are called Bonding Molecular orbitals and
is represented by ΨMO = ΨA + ΨB.
They have lower energy than atomic
orbitals involved. It is similar
to constructive interference occurring in
phase because of which electron
probability density increases resulting in
formation of bonding orbital.
10. Anti-Bonding Molecular Orbitals
When molecular orbital is formed by subtraction o
wave function, the type of molecular orbitals
formed are called Antibonding Molecular
Orbitals and is represented by ΨMO = ΨA - ΨB.
They have higher energy than atomic orbitals. It i
similar to destructive interference occurring out
of phase resulting in formation of antibonding
orbitals. Molecular Orbital formed by subtraction o
overlapping of two s orbitals.
11. It is represented by s* (*) is used to
represent antibonding molecular orbital)
called Sigma Antibonding.
Combination of two atomic orbitals results in
formation of two molecular orbitals, bonding
molecular orbital (BMO) whereas other is anti-
bonding molecular orbital (ABMO).
BMO has lower energy and hence greater
stability than ABMO. First BMO are filled then
ABMO starts filling because BMO has lower
energy than that of ABMO.
12. Rules for Filling of Molecular Orbitals
Certain rules are to be followed while filling up
molecular orbitals with electrons in order to write
correct molecular configurations:
Aufbau Principle – This principle states that those
molecular orbital which have the lowest energy are
Pauli’s Exclusion Principle – According to this principle
each molecular orbital can accommodate maximum of
two electrons having opposite spins.
Hund’s Rule – This rule states that in two molecular
orbitals of the same energy, the pairing of electrons will
occur when each orbital of same energy consist one
13. Equal no. of orbitals Order of Energy
Atomic orbitals of
the Pauli exclusion
principle and Hund's
14. Bond Order
It may be defined as the half of difference between
the number of electrons present in the bonding
orbitals and the antibonding orbitals that is,
Bond order (B.O.) = (No. of electrons in BMO - No.
of electrons in ABMO)/ 2.
Those with positive bonding order are
considered stable molecule while those
with negative bond order or zero bond
order are unstable molecule.
15. Magnetic Behavior: If all the
molecular orbitals in
species are spin paired,
the substance is
diamagneti. But if one or
more molecular orbitals are
singly occupied it is
paramagnetic. For Example,
if we look at CO Molecule, it
is diamagnetic as all the
electron in CO are paired.
17. When we discuss about MOT of hydrogen
molecule then we know that in valance shell of
hydrogen atom have one one electron,
When they combine together they form sigma
There is no any electrons are in
Antibonding molecular orbital.
Both two electrons are occupy bonding
Hydrogen molecule is formed sigma bond by
combination of S-S orbital