Alkanes as saturated hydrocarbons

Alkanes are compounds made of only carbon and hydrogen atoms. A compound containing only these two elements is called a hydrocarbon.

The atoms in an alkane are joined by single covalent bonds: each bond consists of one shared pair of electrons. In particular, there are no carbon–carbon double bonds. The carbon atoms therefore carry as many hydrogen atoms as their arrangement allows, so alkanes are described as saturated hydrocarbons.

Alkanes are generally unreactive, but they can still take part in some reactions. They undergo combustion when they burn in oxygen. They can also undergo substitution with chlorine: in ultraviolet light, a chlorine atom replaces a hydrogen atom in an alkane molecule.

Combustion of alkanes

Alkanes are generally not very reactive, but they can burn in oxygen. This reaction is called combustion and releases energy to the surroundings, mainly as heat.

When there is sufficient oxygen, complete combustion occurs: the carbon in the alkane forms carbon dioxide, and the hydrogen forms water. For example, methane burns in oxygen according to the equation:

In this reaction, methane and oxygen are the reactants; carbon dioxide and water are the products. Combustion is therefore an important exception to the general lack of reactivity of alkanes.