The document provides an overview of Molecular Orbital Theory (MOT) and its postulates, describing how covalent bonds form via the combination of atomic orbitals. It explains the concepts of bonding and anti-bonding molecular orbitals, their characteristics, and the linear combination of atomic orbitals method used to derive them. Additionally, it discusses the differences between atomic and molecular orbitals, as well as the conditions for successful orbital combination.

1. Shri Shivaji Education Society Amravatis
Shri Shivaji Arts, Commerce & Science College Motala,
Dist. Buldana

2. Mr. Bhaskarrao Subhashrao Bhise
Assistant Professor
Shri Shivaji Arts, Commerce & Science College Motala
Dist. Buldana

3. CONTENTS
1
2
3
4
5
Introduction
Postulates/ Sailent features of MOT
Molecular Orbital Theory ( MOT)
Formation of BMO & ABMO
Rules for linear combination of atomic orbital
Mr. B. S. BHISE , Head of Department Shri shivaji College Motala, Dist. Buldana.

4. Introductiontion
1. Many compound contain covalent bonds, For ex. Present in animal and plant
ssuch as oil, proteins, sugar, wood etc.
2. A covalent bond is formed by sharing of electrons between the two atoms in bond
formation.
3. Lewis theory explains covalent bond formation on the basis of tendency of atom
to attain stable noble gas electronic configuration by sharing of electrons.
4. The two wave mechanical theory of covalent bond explained the nature of
covalent bond formation.
( A) Valence Bond Theory ( B) Molecular Orbital Theory

5. Molecular Orbital Theory ( MOT) :-
1. This theory explained by Hund, Mulliken & Lehnard Jones.
2. This theory uses wave function (Ψ ) describe how electron are distrubuted in
molecules.
3. in the same way quantum mechanics use wave function to describe how electron
are distributed in atom.
4. The area in which the probability of finding an electron is high is called
molecular orbital.
5. Molecular orbital can be used for Calculate Geometry, energy levels and other
property of molecules.

6. POSTULATES / SALIENT FEATURES OF MOT:-
1. Molecular orbital are formed by combination of atomic orbital of nearly same
energy and symmetry.
2. In MO theory all the electrons in molecules are considered to be under the
influenced of all the nuclei present in the molecules.
3.The number of molecular orbital is equal to number of atomic orbitals for
combination.
i.e. When two atomic orbital combine to form two molecular orbital
1- lower energy is called Bonding Molecular Orbital ( BMO ) & 2- other higher
energy called as anti-bonding molecular orbital ( ABMO)
4. The shape of molecular orbital depend on shape of combinationof AO.
5. The distribution of electron in molecular orbital is similar to atomic orbital.
Acc. To Aufbau principal, Pauli exclusion, & Hunds rule.
6. The combination of atomic orbital takes places acc. To LCAO method

7. Mr. B. S. BHISE Head department of chemistry Shri shivaji college motala, Dist. Buldana
LCAO apporoximation ( LCAO Method )
1. According to LCAO method ( Linear combination of Atomic Orbital ) molecular orbital
are formed by linear combination of atomic orbital of atoms, which forms molecules.
2. Molecular obtained by adition or subtracting wave function of combination of atomic
orbital.
3. Consider diatomic molecule containing two atom A & B combine with each other .
ΨA and ΨB is wave function of electron. These two atomic orbital combine to form
molecular orbital.
4. According to LCAO method these wave function can be added or substrated to give new
wave function Ψbonding and Ψanti-bonding. Mathematically can be expressed as
ΨMO = ΨA ± ΨB
Ψbonding = ΨA + ΨB …….Addition
Ψantibonding = ΨA - ΨB ……..Subtraking

8. Formation of Bonding Molecular Orbital ( BMO) and Anti-Bonding
molecular Orbital.( ABMO)
(A) Bonding Molecular Orbital ( BMO) :-
1. Formation of BMO by addition of wave function. (ΨA + ΨB )
2. During the formation of BMO electron density increases between the two nuclei.
3. Formed BMO has lower energy than corresponding atomic orbital.
4. It provide favorable condition for formation of bond between atom.
5. Energy can be calculated of BMO is given by
EBMO = E0- β where, E0 is energy of atomic orbital, β = Constant

9. When two Hydrogen atom of two atomic orbital involved in bonding the formation of BMO
can be graphically as shown
+
1s 1s Addition 𝜎1𝑠
Fig. Formation of BMOP by addition of two 1s AO
+
Fig. The electron density for individual Ads and MO
+ o + 0 0+ 0 + 0 0 + 0

10. (B) Anti-Bondinhg Molecular orbital :-
1. Formation of ABMO by substarating of wave function. (ΨA − ΨB )
2. During the formation of ABMO electron density decreases between the two nuclei.
3. Formed ABMO has higher energy than corresponding atomic orbital.
4. It provide unfavorable condition for formation of bond between atom.
5. Energy can be calculated of ABMO is given by
EBMO = E0- β where, E0 is energy of atomic orbital, β = Constant

11. When two Hydrogen atom of two atomic orbital involved in bonding the formation
of BMO can be graphically as shown
-
1s 1s Substraction 𝜎1𝑠 ∗
Mr. B. S. BHISE Head department of chemistry Shri Shivaji College Motala, Dist. Buldana.
+ o + o - 0 o + o + o - o

12. Comparison of atomic orbital and molecular orbital
Atomic Orbital
1. Atomic orbital are space around the
nucleus of atom where is maximun
probability of finding electron.
2. Atomic orbitals are associated with atom.
3. Atomic orbitals are monocentric.
Molecular Orbital
1. Molecular orbital is space around two
or more nuclei where is maximum
probability of finding electron.
2. Molecular orbitals are associated with
molecules and formed by combination of
atomic orbitals.
3. Molecular orbitals are polycentric.

13. Difference between Bonding and Anti-bonding MO
BMO:- ABMO
1. It is formed by LCAO method by
addition of wave number
i.e. ΨA + ΨB
2. It has lower energy than parent AO’s
3. It is stable
4. Electron density increases
5. Actual bonding take place
6. There is a shielding of nuclear
repulsion
1. It is formed by LCAO method by
subtraction of wave number
i.e. ΨA − ΨB
2. It has more energy than parent AO’s
It is unstable
4. Electron density decreases
5. No actual bonding
6. Nuclear repulsion is not shielded.

14. Rules for linear combination of atomic orbitals:-
Atomic orbitals combine resulting formation of molecular orbitals the main conditions are
1. Energy Rule:-
The energy of atomic orbitals combining together must be similar.
According to this rule, homonuclear diatomic molecules will not formed by linear
combination of 1s- orbital of one atom and 2s- orbital of another atom.
Or 2s orbital of one atom and 2p orbital of another atom. Because of 1s, 2s and 2p
orbital different energies.
In the formation of heterodiatomic molecules may be possible.
2. Extent of Overlapping :-
The atomic orbital will combine only if they overlap greater extent.
Greater the overlap of AO greater is the strength of bond formation . This condition is
called as “principle of maximum overlap”

15. 3. Symmetry Rule :-
The two AO’s combining should have same symmetry about the axis.
ex. Pz or py orbital of one atom will not overlap with S- orbital of another atom, MO
will not formed. Because of not same S- orbital and p- orbital.
S +,+ overlap 2pz
s- orbital p- orbital + , - overlap
Fig. A) Permissible Overlapping Fig B) Non Permissible Overlapping
+ + -
-
+

16. T N
Y O U