Hybrid Orbitals

Part 3. sp Hybridization of Carbon

sp² hybridization is best illustrated using ethylene, C₂H₂. The carbon atoms in this molecule are sp hybridized.

Note that each carbon now has only two bonds, and that the bonds about each carbon atom are colinear, with 180^o bond angles throughout. Note also that the C-C bond is a triple bond, i.e. 6 electrons.

 

To make these bonds, the s orbital and one of the p orbitals of carbon are hybridized to form two equivalent sp hybrid orbitals. (Remember for now that this leaves two p orbitals of each carbon un-used.) Each sp orbital looks like the following. It may not at first glance appear to be very different from the sp³ or sp² hybrids, but it does have less p character and more s character than the others. Use the mouse to rotate the figure.

 

When the two sp hybrids are arranged around the carbon nucleus, we have:

 

 

To form the C-C bond, an sp hybrid from one carbon atom overlaps with that of the other, creating a C-C single bond. This type of bond, resulting from the end-on interaction of the two hybrid orbitals, is termed a "sigma" bond. The other two sp hybrids are used to make single bonds with the hydrogens.

Remember those left over p orbitals on each carbon atom? These now overlap to produce two pi bonds between the carbon atoms. These pi bonds and the C-C sigma bond constitute the triple bond between the carbons. Note the extra electron density between the carbons.

Cool, eh?

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