Types of Hybridization
So far we have talked only about single, sigma bonds. We talked about how this results from sp3 hybridization. There are two other very important kinds of hybridization that can also occur.
sp3 hybridization
| Type of hybrid | Diagram | Atomic orbitals used | Number of hybrid orbitals formed | Number of atoms bonded to the C | Geometry |
| sp3 | s, p, p, p | 4 | 4 | tetrahedral |
The first is the sp3 hybridization that we have already talked about. sp3 hybridization results from the combination of the s orbital and all three p orbitals in the second energy level of carbon. It results in four hybrid orbitals and occurs when a carbon atom is bonded to four other atoms. The geometric arrangement of those four hybrid orbitals is called tetrahedral.
sp2 hybridization
| Type of hybrid | Diagram | Atomic orbitals used | Number of hybrid orbitals formed | Number of atoms bonded to the C | Geometry |
| sp2 | s, p, p | 3 | 3 | flat triangular |
Another kind of hybridization uses the s orbital and two of the p orbitals from the second energy level of carbon to form three hybrid orbitals. This kind of hybridization is called sp2 hybridization. It has three hybrid orbitals and there is also an unchanged p orbital that is not shown here. The geometric arrangement of these three sp2 hybrid orbitals is in a flat plane with 120 degree angles between them. The leftover p orbital lies at a 90 degree angle to the hybrid orbitals. If it had been included in this diagram, its two lobes would be pointing directly at and away from you. This kind of hybridization occurs when a carbon atom is bonded to three other atoms. If it is a very simple molecule with just the carbon atom and the other three atoms, it would be a flat triangular molecule. If this is part of a larger molecule, this part would have a flat triangular shape.
sp hybridization
| Type of hybrid | Diagram | Atomic orbitals used | Number of hybrid orbitals formed | Number of atoms bonded to the C | Geometry |
| sp | s, p | 2 | 2 | linear |
There is still a third type of hybridization, it is sp hybridization. In it the s orbital and one of the p orbitals from carbon's second energy level are combined together to make two hybrid orbitals. Those hybrid orbitals form a straight line. There is a 180 degree angle between one orbital and the other orbital. They are exactly opposite one another from the center of the carbon atom. Because this type of sp hybridization only uses one of the p orbitals, there are still two p orbitals left which the carbon can use. Those p orbitals are at right angles to one another and to the line formed by the hybrid orbitals. If they were shown in this diagram, one would go straight up and down and the other would go straight toward and away from you. This kind of hybridization occurs when a carbon atom is bonded to two other atoms.
This is one of the harder concepts to picture. Here is a link to an on-line animation of hybridization that may help you visualize it a little bit more easily. (Do not concern yourself with the sp3d or sp3d2 hybridized orbitals.) This link will open in a new window.
A very important aspect of sp2 and sp hybridization is that they allow carbon atoms to form double and triple bonds.
Comparing Hybrid Types
Let's add to our earlier summary of hybridization by adding the pi bonding aspect to the comparison.
| Type of Hybrid | sp3 | sp2 | sp |
| Atomic orbitals used | s, p, p, p | s, p, p | s, p |
| Number of hybrid orbitals formed | 4 | 3 | 2 |
| Number of atoms bonded to the C | 4 | 3 | 2 |
| Number of sigma bonds | 4 | 3 | 2 |
| Number of left over p orbitals | 0 | 1 | 2 |
| Number of pi bonds | 0 | 1 | 2 |
| Bonding pattern | | - C - | |
\ C = / |
= C = or - C º |
Note that the the number of atoms bonded to the carbon atom and the number of sigma bonds are equal to the number of hybrid orbitals. Also, the number of pi bonds formed is equal to the number of p orbitals that were not hybridized. In each case, the total number of bonds (sigma and pi) and the total number of orbitals (hybrid and p) is four. These are some relationships to keep in mind as you sort through the bonding arrangements and hybridization that occurs in various organic compounds.
