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 180o 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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