A hydrocarbon is a compound made of only carbon and hydrogen atoms. The simplest hydrocarbons have only single bonds, and they are called alkanes.
Alkanes are named by how many carbon atoms are in their chain. The first part of the name counts the carbons, and the ending -ane says the molecule has only single bonds.
| Name | Formula | State | Boils at |
|---|---|---|---|
| methane | CH₄ | gas | −162 °C |
| ethane | C₂H₆ | gas | −89 °C |
| propane | C₃H₈ | gas | −42 °C |
| butane | C₄H₁₀ | gas | −1 °C |
| pentane | C₅H₁₂ | liquid | 36 °C |
| hexane | C₆H₁₄ | liquid | 69 °C |
| heptane | C₇H₁₆ | liquid | 98 °C |
| octane | C₈H₁₈ | liquid | 126 °C |
Look at the formulas. Every carbon in the chain carries 2 hydrogen atoms, and the two carbons at the ends carry one extra each. So an alkane with n carbons has 2n + 2 hydrogens. Chemists write this as CnH2n+2.
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Longer chains cling to each other more, so they boil at higher temperatures. Small alkanes are gases: methane is natural gas, propane is the bottled gas for barbecues and patio heaters, and butane fills lighters and camping stoves. Alkanes burn well, but apart from that they react with very few things.
Remember ethene and ethyne from lesson 2? The ending tells you about the bonds. -ane means only single bonds, -ene means there is a C=C double bond, and -yne means there is a C≡C triple bond. Only the -ane molecules are alkanes.