Mononuclidic element
one of the 22 chemical elements that is found naturally on Earth essentially as a single nuclide (which may, or may not, be a stable nuclide)
A mononuclidic element or monotopic element is a chemical elements that is found naturally on Earth as only one nuclide. Most elements have many nuclides, that is their nuclei may have various numbers of neutrons. The single nuclide of a mononuclidic element may, or may not, be a stable one. There are 21 mononuclidic elements.
