Docsity
Docsity

Prepare for your exams
Prepare for your exams

Study with the several resources on Docsity


Earn points to download
Earn points to download

Earn points by helping other students or get them with a premium plan


Guidelines and tips
Guidelines and tips

Molecular Orbital Theory: Linear Combination of Atomic Orbitals, Lecture notes of Organic Chemistry

Dual nature of electron and Wave function of a molecular orbital.

Typology: Lecture notes

2020/2021

Uploaded on 06/21/2021

myfuture
myfuture 🇺🇸

4.4

(18)

258 documents

1 / 3

Toggle sidebar

This page cannot be seen from the preview

Don't miss anything!

bg1
MOT: LINEAR COMBINATION OF ATOMIC
ORBITALS (LCAO)
Molecular orbital theory is quite successful in solving the mystery of molecules. In
VBT we have learnt that only valence electrons and their corresponding orbitals of
different atoms take part in bonding and form a molecule. The MOT suggests that all
atomic orbitals of different atoms come together and produce molecular orbitals, thus
whole atoms participate in bonding to form a molecule. And these molecular orbitals
are associated with all the nuclei in the molecule (nucleus of all bonded atoms).
Do you ever imagine how do any two atoms combine to form a molecule? Two
different atoms come closer to each other, but their nuclei repel each other and their
electrons are attracted by other's nuclei. Both attractive force and repulsive force work
between them, but at certain distance these forces balance each other. This optimum
distance, where both forces are in equilibrium with each other, is called the bond
length. It means that at this distance these atoms can make a stable bond together.
As I have told you that MOT is based on the dual nature of electron. So here we will
describe an electron occupying an atomic orbital by its wave function ψ and we will
see how MOT finds the wave function of a molecular orbital.
But we will try ourselves first. If we have 2 atoms A and B, each has 2 orbitals and all
of them will combine to produce molecular orbitals. So we have to produce 2+2=4
molecular orbitals. Let’s suppose these orbitals are made up of clay. a1, a2 orbitals and
atom B has b1, b2 orbitals. We can take half of the clay from each orbital from each
atom and mix them to form one molecular orbital like:
pf3

Partial preview of the text

Download Molecular Orbital Theory: Linear Combination of Atomic Orbitals and more Lecture notes Organic Chemistry in PDF only on Docsity!

MOT: LINEAR COMBINATION OF ATOMIC

ORBITALS (LCAO)

Molecular orbital theory is quite successful in solving the mystery of molecules. In VBT we have learnt that only valence electrons and their corresponding orbitals of different atoms take part in bonding and form a molecule. The MOT suggests that all atomic orbitals of different atoms come together and produce molecular orbitals, thus whole atoms participate in bonding to form a molecule. And these molecular orbitals are associated with all the nuclei in the molecule (nucleus of all bonded atoms).

Do you ever imagine how do any two atoms combine to form a molecule? Two different atoms come closer to each other, but their nuclei repel each other and their electrons are attracted by other's nuclei. Both attractive force and repulsive force work between them, but at certain distance these forces balance each other. This optimum distance, where both forces are in equilibrium with each other, is called the bond length. It means that at this distance these atoms can make a stable bond together.

As I have told you that MOT is based on the dual nature of electron. So here we will describe an electron occupying an atomic orbital by its wave function ψ and we will see how MOT finds the wave function of a molecular orbital.

But we will try ourselves first. If we have 2 atoms A and B, each has 2 orbitals and all of them will combine to produce molecular orbitals. So we have to produce 2+2= molecular orbitals. Let’s suppose these orbitals are made up of clay. a 1 , a 2 orbitals and atom B has b 1 , b 2 orbitals. We can take half of the clay from each orbital from each atom and mix them to form one molecular orbital like:

½(a 1 ) + ½(b 1 ) = MO 1 ,

½(a 1 ) + ½(b 1 ) = MO 2 , similarly we can get other 2 MOs.

Or we can proceed through another way. We can mix the clay from all the atomic orbitals and then make new MOs. Like:

a 1 + a 2 + b 1 + b 2 = MO 1 + MO 2 + MO 3 + MO 4

MOT also has two procedures to get wave function of molecular orbital. One way is similar to our first procedure, in which it suggests that atoms come to the equilibrium distance and mix their atomic orbitals to produce molecular orbitals. This approach is called the ‘Linear Combination of Atomic Orbitals’ (LCAO).

Other way is similar to our second procedure, in which MOT suggests that atoms superimpose each other and produce new molecular orbitals and then move apart to their equilibrium distance. This approach is called the ‘United Atom Method’.