Mononuclidic element

The green elements, plus bismuth (orange) and protactinium (red), are mononuclidic.

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: nineteen are stable, and two are radioactive.

Isotopes of mononuclidic elements

• Beryllium-6
• Fluorine-18
• Sodium-23
• Aluminium-27
• Phosphorus-31
• Scandium-45
• Manganese-55
• Cobalt-59
• Arsenic-75
• Yttrium-89
• Niobium-93
• Rhodium-103
• Iodine-127
• Caesium-133
• Praseodymium-141
• Terbium-159
• Holmium-165
• Thulium-169
• Gold-197
• Bismuth-209 (very weakly radioactive)
• Protactinium-231 (radioactive)