This document provides an introduction to molecular orbital theory (MOT). It defines MOT as occurring when individual atomic orbitals combine to form molecular orbitals as electrons are associated with multiple nuclei when atoms bond. The key points covered are: 1) MOT explains questions not answered by valence bond theory, such as why H2 does not exist and why O2 is paramagnetic. 2) Bonding orbitals have lower energy than atomic orbitals and result from constructive interference, while antibonding orbitals have higher energy from destructive interference. 3) MOT is used to explain the bonding in molecules such as H2, O2, CO, and NO.

3. MOLECULAR ORBITAL THEORY
BY
Zameer Ahmed18CH19
QUEST NAWABSHAH

4. REFERANCES OF OUR
PRESENTATION
Knowbee Mastering Organic chemistry.
Parveen Jhambre.
O&I Cemistry of SINDH and PUNJAB
Board.
Professor Davi Explains.
Lectures of Sir Mehmmod Nabi Abbasi.

5. SOME WEBSITES
http://www.chemguide.co.uk/atoms/propert
ies/atomorbs.html
http://www.ch.ic.ac.uk/vchemlib/course/mo
_theory/main.html
http://en.wikipedia.org/wiki/Molecular_orbit
al_theory
http://library.thinkquest.org/27819/ch2_2.sh
tml

6. Aslam0Alaikum to my respectable
teacher and my class fellows and
GOOD MORNING.
Today My presentation on topic
“MOT”.
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
Bonding Orbital,
The orbital having high energy is called
AntiBonding orbital

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
filled first.
 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
electron

13. Equal no. of orbitals Order of Energy
Atomic orbitals of
like energies.
Following both
the Pauli exclusion
principle and Hund's
rule
Principles

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
bond.
There is no any electrons are in
Antibonding molecular orbital.
Both two electrons are occupy bonding
molecular orbital.
Hydrogen molecule is formed sigma bond by
combination of S-S orbital

18. MOT of Hydrogen
H2
 1S1 1S1

20. MOT OF OXYGEN MOLECULE

21. MOT OF CARBON MONO OXIDE

22. MOT OF NITRICOXIDE