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Recall : methane, CH4 – tetrahedral
shape (4 equal covalent bonds)
Carbon has an electron
There is a contradiction
here . . . . . .
Recall: the s orbital shape
ONE s orbital in each energy level
Recall: the p orbital shape
THREE p orbitals in each energy level (beginning n = 2)
Carbon’s valence shell - 2nd energy level orbitals
The 4 orbitals are oriented like so:
This is not a tetrahedral
shape. The 3 p orbitals are at
900 to each other and the s
orbital is “non-directional”
Carbon ground state electron configuration
What is the expected orbital notation of carbon
in its ground state?
Only 2 electrons appear to be available for bonding
Solution – require 4 unpaired electrons
Perhaps carbon “promotes”
one of its 2s electrons…
…to the empty 2p orbital.
BUT. . . this would mean that three of the bonds in a methane
molecule would be identical,
But what about the fourth
Must have a lower bond energy
This was not observed by chemists
“hybridization” theory - What if the s orbital is combined
with three p orbitals to create four equal hybrid orbitals?
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.
Since the 4 hybrid orbitals result from a combination of 1 s
and 3 p orbitals, these hybrids are termed sp3 orbitals.
3 3 3 3
1s 2s 2px 2py 2pz sp sp sp sp
Summary of sp3 hybridization
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
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
sp2 hybridization also occurs in molecules that contain double
covalent bonds. For example, ethene C2H4
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
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
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.
bond Sigma bond
trigonal planar (3 regions of electron density)
Consider the electron configuration of beryllium:
When beryllium bonds with chlorine, VSEPR predicts a
One s orbital hybridizes with 1
p orbitals to form 2 sp orbitals
sp hybridization also occurs in molecules that contain
triple covalent bonds. For example, acetylene C2H2
In ethyne C2H2 each carbon has 2 sp orbitals and 2 un-hybridized
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
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
Show video tutorial acetylene