- A substance which can not be subdivided into smaller units by chemical means. There are over 110 known chemical elements, each with unique properties, and they comprise all matter above the atomic level. The smallest particle that retains all the properties of an element is an atom. All neutral atoms of a given chemical element have the same number of protons and electrons, and if an element has isotopes, the difference between each is the number of neutrons in its nucleus. Also called element (3).
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