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Promethium (Pm)

Promethium is a chemical element of the periodic table with chemical symbol Pm and atomic number 61 with an atomic weight of 145 u and is classed as lanthanide. Promethium is solid at room temperature.

Promethium in the periodic table

Atomic number61
Color Silver
Number of protons61 p+
Number of neutrons84 n0
Number of electrons61 e-
From Wikipedia, the free encyclopediaPromethium, 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.

Physical properties

Phase at STPSolid
Density7.26 g/cm3
Atomic weight145 u

Thermal properties

Melting point1315 K
1041.85 °C
1907.33 °F
Boiling point3273 K
2999.85 °C
5431.73 °F
Heat of vaporization289 kJ/mol

Atomic properties

Electronegativity (Pauling Scale)1.13
Electron affinity12.45 kJ/mol
Oxidation states+2, +3
(a mildly basic oxide)
Ionization energies
  1. 540 kJ/mol
  2. 1050 kJ/mol
  3. 2150 kJ/mol
  4. 3970 kJ/mol

Electron configuration for promethium

Electron configuration
Shorthand configuration
[Xe] 4f5 6s2
Electron configuration
Full configuration
1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d10 4f5 5s2 5p6 6s2
Electron configuration chart
Electrons per shell2, 8, 18, 23, 8, 2
Valence electrons 2
Valency electrons 3
Bohr model
PromethiumElectron shell for Promethium, created by Injosoft ABPm
Figure: Shell diagram of Promethium (Pm) atom.
Orbital Diagram

The history of Promethium

DiscoveryCharles D. Coryell, Jacob A. Marinsky, Lawrence E. Glendenin (1945)
Named byGrace Mary Coryell (1945)
Discovery of promethium
In 1902 Bohuslav Brauner suggested that there was a then-unknown element with properties intermediate between those of the known elements neodymium (60) and samarium (62); this was confirmed in 1914 by Henry Moseley, who, having measured the atomic numbers of all the elements then known, found that atomic number 61 was missing. In 1926, two groups (one Italian and one American) claimed to have isolated a sample of element 61; both "discoveries" were soon proven to be false. In 1938, during a nuclear experiment conducted at Ohio State University, a few radioactive nuclides were produced that certainly were not radioisotopes of neodymium or samarium, but there was a lack of chemical proof that element 61 was produced, and the discovery was not generally recognized. Promethium was first produced and characterized at Oak Ridge National Laboratory in 1945 by the separation and analysis of the fission products of uranium fuel irradiated in a graphite reactor. The discoverers proposed the name "prometheum" (the spelling was subsequently changed), derived from Prometheus, the Titan in Greek mythology who stole fire from Mount Olympus and brought it down to humans, to symbolize "both the daring and the possible misuse of mankind's intellect". However, a sample of the metal was made only in 1963.


List of unique identifiers for Promethium in various chemical registry databases
CAS Number7440-12-2
ChemSpider ID22386
EC number231-121-9
PubChem CID Number23944