Isotope "nuclide", and is still sometimes used in contexts where "nuclide" might be more appropriate, such as nuclear technology and nuclear medicine. An isotope and/or nuclide is specified by the name of the particular element (this indicates the atomic number) followed by a hyphen and the mass number (e.g. helium-3, helium-4, carbon-12, carbon-14, uranium-235 and uranium-239). When a chemical symbol is used, e.g. "C" for carbon, standard notation (now known as "AZE notation" because "A" is the mass number, "Z" the atomic number, and E for element) is to indicate the mass number (number of nucleons) with a superscript at the
Mononuclidic element Mononuclidic element A mononuclidic element or monotopic element is 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). This single nuclide will have a characteristic atomic mass. Thus, the element's natural isotopic abundance is dominated either by one stable isotope or by one very long-lived isotope. There are 19 elements in the first category (which are both monoisotopic and mononuclidic), and 3 (bismuth, thorium and protactinium) in the second category (mononuclidic but not monoisotopic, since they have zero, not one, stable nuclides). A