A chemical element is a substance that cannot be changed, broken down, or decomposed by ordinary chemical or physical methods into a simpler form. A chemical element is composed of atoms, identical and unique for every element, that vary only in their mixture of protons, neutrons, and electrons.

The number of elements known to scientists constantly changes as advances in technology allow the synthesis of heavier elements. As of 2000, the International Union of Pure and Applied Chemistry (IUPAC), an international scholarly scientific organization with the responsibility for naming elements, had named elements as heavy as the element Meitnerium (atomic number 109). Observations of heavier elements (up through atomic number 118) awaited confirmation. Of the recognized elements, 89 occur in a free or combined state in the Earth's crust. The remaining elements are prepared or synthesized in laboratories. Most of the natural elements are found in various combinations with each...