Hydrocarbon

A hydrocarbon is a chemical compound whose molecules contain only carbon (C) and hydrogen (H). It forms the basis of organic chemistry, since carbon can form four bonds, which allows it to create long chains, branches and rings.

Hydrocarbons occur naturally in underground oil: crude oil, natural gas and coal. They are used for energy (when burned) and also as raw materials for plastics, medicines, fertilizers and other chemicals.

Classes

There are two major classes. The aliphatic, which have simple chains or rings, and the aromatic, which contain a specific stable ring structure like benzene. The aliphatic are divided by bond type: alkanes (single bond, for example methane and ethane), alkenes (double bond, for example ethene), and alkynes (triple bond, for example ethyne).

Properties

Hydrocarbons generally do not dissolve in water, because their molecules are non-polar. As chains grow longer, boiling point increases: the shortest, such as methane, are gases; medium-length ones are liquids like petroleum; the longest are waxes or solids. Complete combustion produces carbon dioxide and water; incomplete combustion produces carbon monoxide and soot.

Uses and effects

Oil refineries separate crude oil by a method called distillation to obtain petrol, kerosene, diesel and other products. Burning hydrocarbons is a major source of greenhouse gas carbon dioxide, which is linked to climate change. Oil spills at sea also affect marine life.