Because promethium is artificially created and doesn’t have much use as a critical raw material, discussions on the rare earth elements typically leave off this light rare earth element (LREE). Today, however, we’ll shed some light on this rare element, introducing promethium through interesting and fun facts!

For more information, check out the light rare earth elements (LREEs) as a group, the heavy rare earth elements (HREEs) as a group, and all rare earth elements (REEs).

20 Interesting Facts About Promethium

1. Promethium is a rare earth element with the symbol Pm and atomic number 61, and is the only radioactive lanthanide with no stable isotopes among its 38 known isotopes.
2. Only about 500-600 grams of promethium exist naturally in Earth’s crust at any given time, produced by spontaneous fission of uranium, making it one of the rarest naturally occurring elements.
3. It was the last lanthanide to be discovered, first produced at Oak Ridge National Laboratory in 1945 from uranium fission products (though kept secret initially due to wartime security), with pure metal not isolated until 1963.
4. Named after Prometheus who stole fire from the gods, reflecting both its radioactive nature and the fact humans had to create it artificially.
5. Promethium salts luminesce pale blue or green in the dark due to radioactivity exciting surrounding molecules, with compounds often appearing pink or red.
6. The most common isotope, promethium-147 (half-life 2.6 years), is used in atomic batteries for spacecraft, satellites, pacemakers, and other devices requiring long-term power.
7. Promethium-149 has been studied as a portable X-ray source for medical imaging, as its beta particles can be converted to X-rays.
8. It’s the only element between atomic numbers 1-83 with no stable isotopes, creating a notable gap in the periodic table that puzzled scientists before its discovery.
9. Detected in stellar spectra (particularly HR 465 in Andromeda), confirming theories about element formation in stars through slow neutron capture.
10. Physical properties: solid at room temperature, melting point ~1042°C, boiling point ~3000°C, density ~7.26 g/cm³.
11. Forms typical +3 oxidation state compounds like other lanthanides, exhibiting standard rare earth magnetic properties despite being radioactive.
12. Its beta decay rate remains remarkably constant across extreme temperatures, making it useful for precise timing applications.
13. Chemical properties were largely predicted from periodic table position before experimental confirmation, demonstrating the predictive power of periodic trends.
14. One of only two elements (with technetium) that are both preceded and followed by elements with stable isotopes.
15. Full characterization remains incomplete due to its scarcity and radioactivity, with properties still being investigated.
16. Promethium was once used in luminous paint for watch dials and instrument panels, though it has largely been replaced by tritium due to safety concerns and longer half-life considerations.
17. The longest-lived isotope, promethium-145, has a half-life of 17.7 years and decays by electron capture to neodymium-145, emitting soft X-rays in the process.
18. In nuclear reactors, promethium-147 is produced as a fission product with a yield of about 2.3% from uranium-235, making reactor waste a primary source for commercial production.
19. Promethium can form organometallic compounds and has been incorporated into specialized phosphors that convert its beta radiation into visible light more efficiently than simple luminescence.
20. The element’s ionic radius contracts slightly more than expected across the lanthanide series (part of the “lanthanide contraction”), affecting its coordination chemistry and complex formation compared to neighboring elements.

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