SCH4U – The Chemistry of Covalent Bonding Date_____________________

Orbital Hybridization
One of the most influential chemistry books ever written was The Nature of the Chemical Bond by Linus Pauling (1901-1994). Published in 1939, Pauling was awarded the Nobel Prize in 1954. Pauling received a second Nobel Prize for peace in 1962. Pauling made tremendous contributions to the field of chemistry, and was an outspoken activist against war and nuclear weapons.

If you consider the energy level diagram for carbon it presents a problem to the VB theory. If bonds are formed between orbitals that contain unpaired electrons, how many bonds does it appear carbon can form?

| | 2 | | 1 | |
Since Carbon only has 4 different 4 valence electrons, according to the Aufbau principle, the 2s orbital is filled first, and then the 2p sub shell has 2 orbitals with unpaired electrons. This suggests that Carbon can only form 2 bonds. However Carbon is clearly able to form 4 bonds, as evidenced by any carbon compound (e.g. methane, CH4).

Linus Pauling suggested that carbon is able to create four unpaired orbitals by promoting one electron from the 2s orbital to the empty 2pz orbital. This hybridizes the one 2s and three 2p orbitals together. This configuration is called ‘sp3’.

Like s and p orbitals, the ‘shape’ of sp3 orbitals can be defined by a probability density map of electron location around the nucleus. The shape of a sp3 orbital looks like this:

Since carbon is able to form 4 hybridized orbitals, they form a geometric arrangement called tetrahedral.

1
2
s sp3 1
2
s sp3 In terms of energy, the resulting hybridized orbitals are in between the energy of the s and p subshells. Overall this is a higher energy state than if the atom were unhybridized, therefore atoms are only found in a hybridized state when they are bonded, never on