A chemical element, or simply element, is any substance that cannot be decomposed into simpler substances by ordinary chemical processes. Elements are the fundamental materials of which all matter is composed.
An element is effectively a type of atom that is distinguished by its atomic number; that is, by the number of protons in its nucleus. The term is also used to refer to a pure chemical substance composed of atoms with the same number of protons.
Some of the more common elements are carbon, nitrogen, oxygen and hydrogen. In total, 117 Elements have been observed as of 2007, of which 94 occur naturally on Earth.
Elements with atomic numbers 83 or higher (bismuth and above) are inherently unstable, and undergo radioactive decay. Of the first 82 elements, 80 have stable isotopes. Elements 43 and 61 (technetium and promethium) have no stable isotopes, and decay. The elements from 83 to atomic number 94 that have no stable nuclei, are nevertheless found in nature, either surviving as remnants of the primordial stellar nucleosynthesis which produced the elements in the solar system, or else as produced newly as short-lived daughter-isotopes in the natural decay of uranium and thorium.
All chemical matter consists of these elements. New elements of higher atomic number are discovered from time to time, as products of artificial nuclear reactions.
