Carbon forms four equal hybrid orbitals through sp3 hybridization to allow methane to adopt its tetrahedral electron geometry. This involves one s orbital and three p orbitals combining to form four new hybrid orbitals. Sigma bonds are formed by the head-on overlap of hybrid orbitals. Sp2 hybridization with one s and two p orbitals results in trigonal planar geometries like ethene. Pi bonds in double and triple bonds involve overlap of unhybridized p orbitals above and below the sigma bond.

1. IB Chemistry Power Points
Topic 14 (AHL)
Bonding
www.pedagogics.ca
LESSON
Hybridization
(video tutorial links included)

2. Recall : methane, CH4 – tetrahedral
shape (4 equal covalent bonds)
Carbon has an electron
arrangement 1s22s22p2
There is a contradiction
here . . . . . .

3. Recall: the s orbital shape
ONE s orbital in each energy level

4. Recall: the p orbital shape
THREE p orbitals in each energy level (beginning n = 2)

5. Carbon’s valence shell - 2nd energy level orbitals
The 4 orbitals are oriented like so:
Problem #1
This is not a tetrahedral
shape. The 3 p orbitals are at
900 to each other and the s
orbital is “non-directional”

6. Carbon ground state electron configuration
What is the expected orbital notation of carbon
in its ground state?
Problem #2?
Only 2 electrons appear to be available for bonding

7. Solution – require 4 unpaired electrons
Perhaps carbon “promotes”
one of its 2s electrons…
…to the empty 2p orbital.

8. BUT. . . this would mean that three of the bonds in a methane
molecule would be identical,
But what about the fourth
bond…?
Must have a lower bond energy
This was not observed by chemists

9. “hybridization” theory - What if the s orbital is combined
with three p orbitals to create four equal hybrid orbitals?
“hybridized”
These new orbitals have slightly MORE energy than
the 2s orbital… and slightly LESS energy than the 2p orbitals.
…
But all 4 hybrid orbitals have equal energy.

10. Since the 4 hybrid orbitals result from a combination of 1 s
and 3 p orbitals, these hybrids are termed sp3 orbitals.

11. 3 3 3 3
1s 2s 2px 2py 2pz sp sp sp sp
y
Hybridize
x
o
109.5
z
Summary of sp3 hybridization

12. sp3 hybridization
in methane
CH4

13. Summary of sp3
hybridization

14. Sigma (σ) bonds
The bonds formed in methane between carbon and
hydrogen atoms are called sigma bonds.
As shown in the diagram, a sigma bond is formed by the head
on overlap of two orbitals. THE OVERLAP REGION LIES
DIRECTLY BETWEEN THE TWO NUCLEI. Nuclei can rotate
about a sigma bond. Video tutorial link to ethane

15. sp2 hybridization
Consider the electron configuration of boron:
When boron bonds with hydrogen, VSEPR predicts a
trigonal planar geometry.
One s orbital hybridizes with 2
p orbitals to form 3 sp2 orbitals

16. sp2 hybridization also occurs in molecules that contain double
covalent bonds. For example, ethene C2H4

17. Each carbon : 3 hybridized sp2 orbitals and 1 p orbital
Sigma bond – single bond C-H
Sigma bond – sp2 orbitals: one half of double bond C=C
Pi bond – p orbitals: other half of double bond C=C

18. Pi bonds
A pi bond consists of two p orbitals that overlap above and
below a sigma bond. A double bond always consists of ONE
sigma bond and ONE pi bond.
The molecule cannot be twisted without breaking the pi bond.
Video tutorial ethene

19. Practice
Draw a diagram to show the orbital overlap in the sigma and pi
bonds in a molecule of formaldehyde CH2O. State the shape of
the molecule and the arrangement of negative charge centers
around the central atom.

20. Formaldehyde
2 Lone
Pairs
 bond Sigma bond
trigonal planar (3 regions of electron density)

21. sp hybridization
Consider the electron configuration of beryllium:
When beryllium bonds with chlorine, VSEPR predicts a
linear geometry.
One s orbital hybridizes with 1
p orbitals to form 2 sp orbitals

22. sp hybridization
sp hybridization also occurs in molecules that contain
triple covalent bonds. For example, acetylene C2H2

23. In ethyne C2H2 each carbon has 2 sp orbitals and 2 un-hybridized
p orbitals.
The single bond between carbon and hydrogen is a sigma bond.
The triple bond between the two carbons consists of a sigma bond
between two sp2 orbitals and two pi bonds between the two sets of
p orbitals.

24. The two pi bonds are in different planes 900 to each other . A
triple bond always consists of ONE sigma bond and TWO pi
bonds. The molecule cannot be twisted without breaking the
pi bonds.
Show video tutorial acetylene