1.6 Multiplicity

Not all bonds are single. It is possible for two atoms to share more than one bond, forming a double or triple bond. This is called the bond's multiplicity. Here's a molecule of acetylene, showing a triple bond between the two carbon atoms. Note each carbon atom only has one hydrogen, since three of the four bonds are satisfied by the other carbon atom.

Two atoms of oxygen can double bond together, forming O₂, and two atoms of nitrogen can form a triple bond and make N₂. These are diatomic molecules, and both nitrogen and oxygen are diatomic. The air we breathe is mostly a mixture of N₂ and O₂, and many gaseous elements are diatomic at standard temperature and pressure, including hydrogen and chlorine.

Hydrocarbons that contain only single bonds are called saturated, meaning each carbon atom has the maximum number of hydrogen atoms that it can hold.

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