Chemistry - Crude Oil

Crude oil formed over a long period of time - millions of years in fact. It formed from the remains of dead sea creatures and plants that rotted down anaerobically (with little or no oxygen) as they became buried with sediments on ancient sea beds. The oil is trapped underground by layers of impermeable rocks and is extracted from the ground by drilling oil wells.

But what is the chemistry of crude oil? Well, it is a mixture of thousands of different chemicals which are mainly hydrocarbons. These are covalently bonded molecules made mainly from the elements hydrogen and carbon, in fact, most are only made from those two elements and are that is why they are called hydrocarbons.

The main types of hydrocarbon in crude oil come from the family of chemicals known as the alkanes - for example, octane, an important component of the gasoline that we use as fuel for cars. The larger alkanes with carbon chain lengths of over 35 atoms are soft solids and are used in the construction industry for roofing and roads.

Crude oil is also always associated with another fossil fuel, gas, because some of the molecules of the alkane family are very small. Small covalently bonded molecules are often gasses at room temperature. Natural gas is methane, the simplest alkane, and it is piped from the oil fields of the north sea to homes and businesses all over Britain.

But chemistry allows us to use crude oil for more than just fuel. There is more bitumen than can be used. To save throwing it away, it can be 'cracked'. This involves using heat and catalysts to break down the longer carbon chains into smaller molecules, including petroleum and molecules like ethene, which can be used to make plastics.