A hydrocarbon is any compound containing only carbon and hydrogen atoms. The form and properties of hydrocarbons vary widely depending on the number of carbon atoms in the molecule and their arrangement.
The shortest hydrocarbons are gases- methane, ethane, and propane. Hydrocarbons with 7-8 carbons, heptane and octane, are thin liquids and the main components of gasoline. Longer unsaturated chains are viscous liquids while very long chains, known as polyethylene, are solids.