Composition of Matter

Core concept

An element is a pure substance made of only one type of atom, like oxygen, gold, or hydrogen, and cannot be broken down further chemically.

How it works

A compound is formed when two or more elements chemically combine in fixed proportions, like water (H2O) or carbon dioxide (CO2).

Why it matters

A mixture is a combination of two or more substances that are physically combined, not chemically bonded, like sand and water.

Key detail

Mixtures can be homogeneous (uniform throughout, like saltwater) or heterogeneous (non-uniform, like a salad), unlike compounds with fixed composition.