Promethium is the rarest lanthanide. Any promethium atoms that were in the Earth's rocks decayed billions of years ago. Therefore, promethium is produced artificially in nuclear reactors. Being highly radioactive, it is used in some missiles, as it converts this radioactivity into electrical energy. Promethium is also used as an additive to make some paints glow in the dark.

Summary of properties (Pm)

Atomic weight[145]
Discoverer (year)Marinsky, J. A. & Glendenin, L. E. (1945)
Natural formmetallic solid (hexagonal)
Electron configuration[Xe] 45 6s2
Melting point (ºC)1100
Boiling point (ºC)3000
Abundance in earth's crust (ppm)<0.001
Isotope (abundance)
Density g/cm37.3
Van der Waals radius (pm)238
Covalent radius (pm)186
Electronegativity (Pauling)
Vaporization enthalpy (kJ/mol)-
Enthalpy of fusion (kJ/mol)7.70
Specific heat capacity (J/g·K) at 25ºC and 1 atm-
Thermal conductivity (W/cm·K) at 25ºC and 1 atm0.150
Oxidation state+3
Electron affinity (eV)
1st Ionization potential (eV)5.5820

Back to the Periodic Table of the Elements.