Promethium
Symbol |
Name |
Atomic Number |
Atomic Weight |
Group Number |
Pm |
Promethium |
61 |
(145) |
|
Standard Sate: solid at 298 K
Color: metallic
Great care is required while handling promethium as a consequence of its radioactivity. Promethium salts luminesce in the dark with a pale blue or greenish glow, due to their high radioactivity.
(Pm), chemical element, only rare-earth metal of transition Group IIIb
of the periodic table not detected in nature. Conclusive chemical proof
of the existence of promethium, the last of the rare-earth elements
to be discovered, was obtained (1947) by J.A. Marinsky, L.E.
Glendenin, and C.D. Coryell, who isolated the radioactive isotope
promethium-147 (2.7-year half-life) from uranium fission products at
the research site at Oak Ridge, Tenn. Identification was firmly
established by spectroscopy. Earlier investigators thought that they
had found the element with atomic number 61 in naturally occurring
rare earths and had prematurely called it illinium and florentium.
Promethium-147 is effectively separated from the other rare-earth
fission products by an ion-exchange method. Its soft beta radiation is
converted to electricity in miniature batteries formed by sandwiching
promethium between wafers of a semiconductor such as silicon;
these batteries operate in extreme temperatures for five years.
Promethium has also been prepared by slow neutron bombardment
of the isotope neodymium-146; the resultant isotope, neodymium-147,
decays by electron emission to promethium-147. The metal itself
was first prepared (1963) by reduction of the fluoride, PmF3, with
lithium.
All of the isotopes of promethium are unstable; the longest lived is
promethium-145 (18-year half-life). Because of the short half-lives
of its isotopes, any promethium that might result from spontaneous
fission of uranium in uranium ores would occur in infinitesimal
concentrations. The physical and chemical properties of promethium
are those of a typical rare earth. It is trivalent in its compounds and
solutions, most of which are pink or rose. atomic number 61 stablest
isotope (145) melting point 1,080 C boiling point 2,460 C specific
gravity -- valence 3 electronic config. 2-8-18-23-8-2 or (Xe)4f
55d06s2
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