![]() Because each carbon in acetylene has two electron groups, VSEPR predicts a linear geometry and and H-C-C bond angle of 180 o. The carbon-carbon triple bond in acetylene is the shortest (120 pm) and the strongest (965 kJ/mol) of the carbon-carbon bond types. This difference in formation leads to a difference in strength. Sigma bonds are formed by direct head to head overlap between orbitals while pi bonds are formed by side to side overlap, usually between p orbitals. These two perpendicular pairs of p orbitals form two pi bonds between the carbons, resulting in a triple bond overall (one sigma bond plus two pi bonds).Īcetylene is said to have three sigma bonds and two pi bonds. The main differences between sigma and pi bonds has to do with their formation and strength. Each carbon atom still has two half-filled 2 p y and 2 p z orbitals, which are perpendicular both to each other and to the line formed by the sigma bonds. The C-C sigma bond is formed by the overlap of one sp orbital from each of the carbons, while the two C-H sigma bonds are formed by the overlap of the second sp orbital on each carbon with a 1 s orbital on a hydrogen. The 2 p y and 2 p z orbitals remain non-hybridized, and are oriented perpendicularly along the y and z axes, respectively. ![]() In an sp-hybridized carbon, the 2 s orbital combines with the 2 p x orbital to form two sp hybrid orbitals that are oriented at an angle of 180°with respect to each other (eg. In the hybrid orbital picture of acetylene, both carbons are sp-hybridized. Finally, lets consider dative covalent bonds. Likewise, because triple bonds contain a sigma bond and two pi bonds, they are stronger still. ![]() However, because a double bond contains a sigma bond and a pi bond, it is overall significantly stronger than a single sigma bond on its own. ![]() The carbon-carbon triple bond is only 1.20Å long. Pi bonds are much weaker than sigma bonds. This molecule is linear: all four atoms lie in a straight line. Consider, for example, the structure of ethyne (another common name is acetylene), the simplest alkyne. \)įinally, the hybrid orbital concept applies well to triple-bonded groups, such as alkynes and nitriles. ![]()
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