Crude Oil, Hydrocarbons and Alkanes

This lesson introduces organic chemistry as covered in the AQA GCSE Combined Science Trilogy (8464) specification. You will learn about crude oil as a finite resource, what hydrocarbons are, the alkane homologous series, and how the properties of hydrocarbons change with chain length.

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What Is Crude Oil?

Crude oil is a fossil fuel formed over millions of years from the remains of ancient marine organisms (plankton) that were buried under layers of sediment. Heat and pressure transformed these remains into a complex mixture of hydrocarbons.

Crude oil is:

• A finite (non-renewable) resource — it is being used up faster than it forms.
• A mixture of many different hydrocarbons.
• The basis of the modern petrochemical industry.

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What Are Hydrocarbons?

A hydrocarbon is a compound made up of hydrogen and carbon atoms only.

Most of the hydrocarbons in crude oil are alkanes.

Key Definition: A hydrocarbon contains only hydrogen and carbon atoms bonded together.

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The Alkane Homologous Series

The alkanes are a family (homologous series) of hydrocarbons with the general formula:

$C_nH_{2n+2}$Cn​H2n+2​

where n is the number of carbon atoms.