Pure substances

'Pure' has a specific meaning in chemistry.

A pure substance is a single element or compound not mixed with any other substance.

A mixture contains two or more different substances mixed together, usually easy to separate.

Pure substancesMixtures
Diamond only contains the element carbon.Air is a mixture of oxygen, carbon dioxide, nitrogen and other trace gases.
Water only contains the compound water.Mineral water is a mixture of water and dissolved salts.
Table salt only contains the compound sodium chloride.Milk is a mixture of water, lactose, fat and minerals such as salt.

Here are some examples of pure substances and mixtures.

Chemical substance table