1. Valence Bond Theory
Linus Carl Pauling (February 28, 1901 – August 19, 1994)

2. Valence Bond Theory
The half filled orbital of one atom overlaps a half filled orbital of a second atom to form a full orbital with two electrons spinning in opposite directions.
The bonding atoms arrange themselves in order to maximize the overlap of the half-filled orbitals.
Maximum overlapping of the orbitals creates a bonding orbital with a lower energy and increased stability.

3. Valence Bond Theory
The combination of electrostatic repulsion and opposing magnetic fields (due to the electron’s spin) creates the stability associated with a bonding orbital.
Electron Spin
Negative charge
Electrostatic repulsion
Negative charge
Electron Spin
“North” magnetic field
Magnetic attraction
“South” magnetic field

4. Valence Bond Theory
During this process, two atoms approach each other and allow their half filled orbitals to overlap and form the stability of a filled bonding orbital.

5. PROBLEMS WITH LEWIS THEORY

6. Hybrid Orbitals
In some situations a more advantageous bonding scenario can be established by promoting electrons from a full orbital to a similar empty orbital to create two half filled orbitals that are available for bonding.
The resulting orbital is a mixture of the two original orbitals and is called a hybrid orbital.
For eg. What is the simplified energy level diagram (ie. Valence electrons) for Carbon?

7. Each hybrid orbital is called an “sp3” orbital
One s e- is promoted to the empty p orbital
This causes the energy of all 4 orbitals to shift:
The energy of the p orbitals is reduced slightly
The energy of the s orbital is increased slightly
Each orbital is a hybrid of 1 “s” and 3 “p” orbitals
Each hybrid orbital is called an “sp3” orbital
The new hybrid orbitals are free to become involved in bonds by overlapping with other half filled valence orbitals.

8. Hybridization C (z = 6) C (z = 6) C (z = 6) C (z = 6) C (z = 6)1s 2s 2p
C (z = 6) 1s
sp3
C (z = 6)
sp3 hybridization 1s 2s 2p
C (z = 6) 1s
sp2
C (z = 6)
sp2 hybridization p 1s 2s 2p
C (z = 6) 1s sp
C (z = 6)
sp hybridization p 1s 2s 2p
C (z = 6)

9. Linus Pauling and Hybrid Orbitals

10. Remember VSEPR…

11. sp3 Hybrid atomic orbitals

12. sp3 hybrid orbitals in CH4

13. sp2 Hybrid atomic orbitals

14. sp2 hybrid orbitals in BF3

15. sp hybrid orbitals in BeF2

16. sp3d and sp3d2 hybridization

17. Double & Triple Bonds
Sigma (s) bonds – The “end-to-end” overlapping of half filled orbitals to make a full bonding orbital of lower energy level (i.e. – more stable) They occur between “s”, “p” and hybrid orbitals (“sp”,“sp2” & “sp3”) to make single covalent bonds.

18. Double & Triple Bonds
Pi (p) bonds – The “side-to-side” overlapping of half filled “p” orbitals to make more stable filled bonding orbitals.

19. Double & Triple Bonds
A combination of “p” and “s” bonds makes double and triple bonds.
Single bonds Sigma only (s)
Double bonds 1 Sigma (s) and 1 Pi (p)

20. Triple bonds 1 Sigma (s) and 2 Pi (p)
Double & Triple Bonds
A combination of “p” and “s” bonds makes double and triple bonds.
Sigma (s ) bond
Pi (p ) bond
Pi (p ) bond
Triple bonds 1 Sigma (s) and 2 Pi (p)