|Group||Lanthanides||Melting point||1042°C, 1908°F, 1315 K|
|Period||6||Boiling point||3000°C, 5432°F, 3273 K|
|Block||f||Density (g cm−3)||7.26|
|Atomic number||61||Relative atomic mass|||
|State at 20°C||Solid||Key isotopes||145Pm, 147Pm|
|Electron configuration||[Xe] 4f56s2||CAS number||7440-12-2|
|ChemSpider ID||22386||ChemSpider is a free chemical structure database.|
- Promethium is a chemical element with the symbol Pm and atomic number 61 in the periodic table.
- 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.
- Most of the element is used only for research purposes, except for promethium-147, which can be found outside laboratories. This isotope does not emit gamma rays, and its radiation has a relatively small penetration depth into matter and a relatively long half-life.
- Promethium is used in pacemakers. Some signal lights use a luminous paint containing phosphor that absorbs the beta radiation emitted by promethium-147 and emits light.
- Chemically, promethium is a lanthanide, which forms salts when combined with other elements. It shows only one stable oxidation state of +3.
- Since traces of the element in nature is exceedingly scarce, the element is typically synthesized by bombarding enriched uranium with thermal neutrons to produce promethium-147.
- Promethium salts have a pink or red color that colors the surrounding air with a pale blue-green light.
- There is a strange star HR 465 in the Andromeda galaxy that contains a lot of Promethium. It is very radioactive and rare, so it is little studied: its chemical and physical properties are not well defined.