Crude Oil and Hydrocarbons


Hydrocarbons are compounds that contain only hydrogen and carbon atoms. These atoms are joined together in chains and rings. Hydrocarbons can be either saturated or unsaturated.

Two molecular diagrams: The first shows four 'C' circles in a straight line, each connected to two 'H' circles, labelled 'saturated compounds'. The second is identical but includes two double bonds, labelled 'unsaturated compounds'.
  • In this image, the carbon atoms are red, and the hydrogen atoms are grey

Homologous series

To better understand hydrocarbons, scientists have organised them into groups called homologous series. A homologous series is a family of hydrocarbons that have similar properties and share the same general formula. This means that chemically, they all behave in the same way and have similar reactions, including having the same functional group of atoms.

However, hydrocarbons in a homologous series show a gradual variation in physical properties, such as melting and boiling points.

  • For example, as the number of carbon atoms in a hydrocarbon increase, so does its boiling point. This means that hydrocarbons with longer carbon chains have higher boiling points than those with shorter chains.

Crude Oil

Crude oil, also known as petroleum, is a complex mixture of hydrocarbons that is found deep beneath the Earth’s surface. It formed naturally over millions of years from the remains of dead plants and animals. This process involved high temperatures and pressures.

Three sections showing the timeline of oil and gas formation: The first shows marine organisms and plants from '300-400 million years ago'. The second displays organism remains under sand and sediment from '100 million years ago'. The final section, labelled 'today', depicts machinery extracting oil and gas.

The appearance of crude oil can vary, but it is typically a liquid substance that we can extract by drilling into the ground. Once extracted, the different hydrocarbons in the mixture can be separated.

However, it’s important to note that crude oil is a finite resource. It took millions of years to form and we are using it up much faster than it is being replenished. This means that if we continue to burn crude oil as a fuel for energy production, it will eventually run out.