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. Promethium shows only one stable oxidation state of +3; however, a few +2 compounds may exist.