In chemistry, a free element is a chemical element that is not combined with or chemically bonded to other elements. Examples of elements which can occur as free elements include the oxygen molecule (O2) and carbon. All atoms of free elements have an oxidation number of 0.
- A. Earnshaw and Norman Greenwood. Chemistry of the Elements (Second Edition) ISBN 978-0-7506-3365-9. Mentions "free element" 30 times, for example, "Oxygen is the most abundant element on the earth's surface. It occurs both as a free element and in combination with innumerable compounds." and "Carbon occurs both as a free element and in combined form."
- IUPAC, Compendium of Chemical Terminology, 2nd ed. (the "Gold Book") (1997). Online corrected version: (2006–) "Oxidation state".
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