Some of the substances we encounter in everyday life are elements.

• Some of the substances we encounter in everyday life are elements.
• Most are not elements—they are compounds.
• Free atoms are rare in nature.
• A compound is different from a mixture of elements.
• In a compound, the elements combine in fixed, definite proportions.
• In a mixture, they can have any proportions whatsoever.

Many Natural Substances Are Compounds