Question #b497b

1 Answer
Ernest Z. · Wendy K.
Jan 27, 2014

To count sigma and pi bonds, first you need to know how many single, double and triple bonds are present in the molecule.

Explanation:

A single bond contains one sigma bond (direct head-on overlap of orbitals).

www.chem1.com

For example, the #"C-C"# sigma bond in ethane is formed by the head-on overlap of two #sp^3# orbitals. The C-H sigma bonds are formed by #s"-"sp^3# overlap.

A double bond contains one sigma bond and one pi bond (side-on overlap of #p# orbitals).

wps.prenhall.com

In ethylene, the #"C=C"# double bond consists of a sigma bond and a pi bond. The sigma bond is formed by the head-on overlap of two #sp^2# orbitals. The pi bond is formed by the side-on overlap of two #2p# orbitals.

A triple bond contains one sigma bond and 2 pi bonds.

www2.chemistry.msu.edu

In acetylene, the #"C≡C"# triple bond consists of a sigma bond and two pi bonds. The sigma bond is formed by the head-on overlap of two #sp# orbitals. The pi bonds are formed by the side-on overlap of #2p# orbitals.

It's just that simple.

Here's a video on counting sigma and pi bonds.

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