Symbol: Pm
Atomic number: 61
Category: lanthanides
Group: n/a
Period: 6
Block: f
Atomic weight: [145] g/mol
Electrons per shell: 2, 8, 18, 23, 8, 2
CAS number: 7440-12-2
Phase: solid
Density: 7.26 kg/dm3 (near room temperature)
Melting point: 1315 K (1042 C, 1908 F)
Boiling point: 3273 K (3000 C, 5432 F)
Crystal structure: hexagonal
Oxidation states: 3
Electronegativity: 1.13 (Pauling scale)
Name's origin: Prometheus
Name's meaning: the Titan, in Greek mythology, who stole the fire from Mount Olympus and brought it down to mankind - the name was suggested by the discoverer's wife, who felt that they were stealing fire from the gods
- is notable for being the only other exclusively radioactive element besides technetium which is followed by chemical elements that have stable isotopes
- its longest lived isotope Pm-145 is a soft beta emitter with a half-life of 17.7 years
- does not emit gamma rays, but beta particles impinging on elements of high atomic numbers can generate X-rays
- exists in two allotropic forms, and its chemistry is similar to other lanthanides
- promethium salts luminesce in the dark with a pale blue or greenish glow, due to their high radioactivity
- is used as a beta radiation source for thickness gauges, in a nuclear battery and in the future, portable X-ray sources
- can be formed in nature as a product of spontaneous fission of uranium-238 and alpha decay of europium-151
- it was calculated that the equilibrium mass of promethium in the Earth's crust is about 560 g due to uranium fission and about 12 g due to the recently observed alpha decay of europium-151