Promethium, originally prometheum, is a chemical element with the symbol Pm and atomic number 61. All of its isotopes are radioactive; it is one of only two such elements that are followed in the periodic table by elements with stable forms, a distinction shared with technetium. Chemically, promethium is a lanthanide, which forms salts when combined with other elements.
Three reasons Promethium stands out
- 1
A rare, radioactive element, used in some nuclear batteries.
- 2
It is the only lanthanide with no stable isotopes, meaning it does not exist in meaningful quantities in nature.
- 3
Its existence was predicted by quantum theory decades before a single atom was ever experimentally confirmed.
A rare earth with no stable isotope
Promethium is the only lanthanide with no stable isotopes. Tiny natural traces arise from radioactive processes, but useful quantities are made in reactors. Its beta radiation has powered specialized long-life batteries and luminous devices, though scarcity and shielding requirements keep its applications narrow.