More Bonds

Not all bonds are the same. So far we've only seen single bonds, but there are also double and triple bonds. We can represent a double bond with an equals sign, for example in the condensed formula of ethylene, which is CH₂=CH₂. Notice that the two carbon atoms only have two hydrogens each, instead of 3. This is because for each carbon atom, two of its bonds are to the other carbon, so it only has 2 available bonds for hydrogen.

Another molecule that has double bonds is carbon dioxide or CO₂. Its condensed formula is O=C=O. The two oxygens have both their bonds with the carbon atom, so there aren't any more available bonds for anything else. All four of the carbon's bonds are to oxygen atoms, so it doesn't have any spare bonds for anything else.

Triple bonds occur in molecules like acetylene: CH≡CH, and hydrogen cyanide HC≡N. Each carbon has three out of four bonds connected to another carbon or to a nitrogen, so only one bond is available for hydrogen. The nitrogen has all three bonds connected to a carbon, so no bonds are available for other atoms.

The nitrogen and oxygen in the air is made up of molecules with these kinds of bonds in them. Oxygen forms molecules of O₂ with a double bond like so: O=O. Nitrogen forms N₂ with a triple bond: N≡N. Both elements are said to be diatomic. Some other elements are also diatomic, including chlorine (Cl-Cl).

Here are the structures of carbon dioxide and hydrogen cyanide:

O=C=O	CO2	H-C≡N	HCN

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