1. Chemical Bonding Mr. Sonaji V. Gayakwad Asst. professor
Dept of chemistry
Mrs.K.S.K. College,Beed

2. Theories of Covalent Bonding
Valence Bond (VB) Theory and Orbital Hybridization
The Mode of Orbital Overlap and the Types of Covalent Bonds
Molecular Orbital (MO)Theory and Electron Delocalization

3. Valence Bond Theory
Linus Pauling and others applied the principles of quantum mechanics to molecules
They reasoned that bonds between atoms would occur when the orbitals on those atoms interacted to make a bond
The kind of interaction depends on whether the orbitals align along the axis between the nuclei, or outside the axis

4. Orbital overlap and spin pairing in three diatomic molecules.
Hydrogen, H2
Hydrogen fluoride, HF
Fluorine, F2

5. Bond Angles in Carbon Compounds
electron configuration = 1s22s22p2
2p orbitals with one
electron in each.
Can p orbitals with one
electron in each find
the place where the
3rd p orbital should
be?
Orbitals with one
electron in each will
overlap to form single
bonds.
If they can, the bond angles
should be 90o.
But…the bond angles are
109.5o!

6. To adjust for these inconsistencies, it was postulated that the valence atomic orbitals could hybridize before bonding took place
one hybridization of C is to mix all the 2s and 2p orbitals to get four orbitals that point at the corners of a tetrahedron

7. Hybrid Orbitals
The number of standard atomic orbitals combined = the number of hybrid orbitals formed
combining a 2s with a 2p gives two 2sp hybrid orbitals
H cannot hybridize!!
its valence shell only has one orbital
The number and type of standard atomic orbitals combined determines the shape of the hybrid orbitals
The particular kind of hybridization that occurs is the one that yields the lowest overall energy for the molecule

8. Carbon Hybridizations
Unhybridized    2s 2p
sp hybridized    
2sp 2p
sp2 hybridized    
2sp2 2p
sp3 hybridized    
2sp3

9. sp3 Hybridization Atom with four electron groups around it
tetrahedral geometry
109.5° angles between hybrid orbitals
Atom uses hybrid orbitals for all bonds and lone pairs

11. Bonding with Valence Bond Theory
According to valence bond theory, bonding takes place between atoms when their atomic or hybrid orbitals interact
“overlap”
To interact, the orbitals must either be aligned along the axis between the atoms, or
The orbitals must be parallel to each other and perpendicular to the interatomic axis

12. Methane Formation with sp3 C

13. Ammonia Formation with sp3 N

16. Orbital Diagrams of Bonding
“Overlap” between a hybrid orbital on one atom with a hybrid or nonhybridized orbital on another atom results in a s bond
“Overlap” between unhybridized p orbitals on bonded atoms results in a p bond

18. CH3NH2 Orbital Diagram s s sp3 C         sp3 N s s s s s  
1s H
1s H
1s H
1s H
1s H

19. Formaldehyde, CH2O Orbital Diagramp  
p C
p O s
sp2 C      
sp2 O s s  
1s H
1s H

20. The sp2 hybrid orbitals in BF3.

21. Hybrid orbitals overlap to form a s bond.
Unhybridized p orbitals overlap to form a p bond.

22. HCN Orbital Diagram 2p    
p C
p N s
sp C    
sp N s 
1s H

24. sp3d Atom with five electron groups around it
trigonal bipyramid electron geometry
Seesaw, T–Shape, Linear
120° & 90° bond angles
Use empty d orbitals from valence shell
d orbitals can be used to make p bonds

28. Molecular shape and e- group arrangement
The conceptual steps from molecular formula to the hybrid orbitals used in bonding.
Step 1
Step 2
Step 3
Molecular shape and e- group arrangement
Molecular formula
Lewis structure
Hybrid orbitals

29. Molecular Orbital Theory
In MO theory, we apply Schrödinger’s wave equation to the molecule to calculate a set of molecular orbitals
in practice, the equation solution is estimated
we start with good guesses from our experience as to what the orbital should look like
then test and tweak the estimate until the energy of the orbital is minimized
In this treatment, the electrons belong to the whole molecule – so the orbitals belong to the whole molecule
delocalization