CH 106 - Lesson 2
Home Up Hybridization Covalent Bonding Sigma Bonds Types of Hybridization Double Bonds Pi Bonds Triple Bonds Comparing Hybrid Types Valence


Triple Bonds


We can also have triple bonds between carbon atoms. The drawing below illustrates a few important characteristics of a molecule with a triple bond between two carbon atoms. The first is shape. Four atoms, the two carbon atoms and the two atoms bonded to them, lie in a straight line. The second is lack of rotation. Actually, this is not terribly important because even if you could rotate the carbon atoms around the triple bond, the shape would not change. Nevertheless, no rotation can occur at the triple bond.
Describing the structure of a triple bond requires another excursion into hybridization in order to explain how these triple bonds come about.

Diagram of bonding in ethyne. [62orb10.JPG]

The triple bond is made up of one sigma bond and two pi bonds. Notice that each of the carbon atoms is bonded to two other atoms. Each of those carbon atoms formed two sigma bonds using two hybrid orbitals. The formation of the two hybrid orbitals required that an s and a p orbital were combined and rearranged. The result was two sp hybrid orbitals, each pointing away from one another, and two leftover p orbitals, each at right angles to everything else. The carbon atoms come close enough to one another for the hybrid orbitals to overlap and form sigma bonds. These are shown as the dark shaded areas lined up right through the center of the molecule. As this happens, the p orbitals also overlap and form two pi bonds, which are shown as the lighter shaded areas. One of those pi bonds is shown above and below. The other pi bond is shown to one side and back to the other side of the central sigma bond.

The following pages in this section will compare the different types of hybridization and how they relate to bonding in organic compounds.


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