Promethium stands as one of the most enigmatic elements in the periodic table, a radioactive lanthanide that has captivated scientists for over a century. Named after the Greek Titan Prometheus who stole fire from the gods and gave it to humanity, promethium embodies both the promise and peril of scientific discovery. As the only rare earth element with no stable isotopes, promethium’s story is one of persistent scientific pursuit, false claims, wartime secrecy, and ultimately, groundbreaking discovery. From its theoretical prediction in 1902 to recent breakthroughs in understanding its chemical properties in 2024, promethium has challenged researchers to push the boundaries of analytical chemistry and nuclear science. This elusive element, existing in mere grams on Earth at any given time, has nonetheless found remarkable applications in nuclear batteries, luminous paints, and thickness gauges, proving that even the rarest of elements can illuminate our understanding of the natural world.

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). The complete history of all 17 rare earth elements can be found here.

Read about the use of rare earths in quantum computing here.

A History Of Promethium

The history of promethium spans over a century of scientific investigation, marked by theoretical predictions, false claims of discovery, and eventual isolation during the Manhattan Project. This chronology traces promethium’s journey from a predicted gap in the periodic table to its modern applications and recent chemical characterization, revealing how this radioactive lanthanide has challenged and advanced our understanding of rare earth chemistry.

Chronology

• 1902 – Czech chemist Bohuslav Brauner predicted the existence of promethium, suggesting there was an unknown element with properties intermediate between neodymium (element 60) and samarium (element 62) [1, 3, 5, 9, 10, 11, 13, 14, 17, 23]
• 1914 – British physicist Henry Moseley confirmed Brauner’s prediction by measuring atomic numbers of all known elements using X-ray spectroscopy, finding that atomic number 61 was missing from the periodic table [1, 11, 13, 14]
• 1924 – Italian chemists Luigi Rolla and Lorenzo Fernandes at the Royal University in Florence claimed to have discovered element 61 and proposed the name “florentium” after their city, depositing their results in a sealed envelope with the Accademia dei Lincei in Rome [1, 10, 11, 13, 15, 17]
• 1926 – B. Smith Hopkins, Len Yntema, and a student named Harris at the University of Illinois published their claim of discovering element 61, proposing the name “illinium” after their state [1, 10, 11, 12, 13, 15, 17]
• 1926 – The Italian team of Luigi Rolla published their work on “florentium,” claiming priority based on their 1924 sealed envelope [1, 10, 11, 12, 13, 15, 17]
• 1927 – A debate over naming priority between “florentium” and “illinium” played out in the journal Nature, with neither claim ultimately being substantiated [16]
• 1934 – Josef Mattauch formulated the isobar rule, indirectly confirming that element 61 was unable to form stable isotopes [1, 18, 22]
• 1938 – H. B. Law and colleagues at Ohio State University conducted nuclear experiments producing radioactive nuclides that were not neodymium or samarium isotopes, proposing the name “cyclonium” after the cyclotron used [1, 12, 14, 18, 19, 20, 21, 22]
• 1939 – The 60-inch cyclotron at the University of California was used in attempts to produce promethium, though results were not proven [23]
• 1941 – Ohio State University researchers produced nuclides attributed to element 61 with the name “cyclonium” proposed, but chemical proof was lacking and the discovery was not widely recognized [1, 14, 18]
• 1945 – Jacob A. Marinsky, Lawrence E. Glendenin, and Charles D. Coryell at Oak Ridge National Laboratory (then Clinton Laboratories) produced and characterized promethium by separation and analysis of uranium fission products in a graphite reactor [1, 2, 3, 4, 6, 7, 10, 11, 12, 13, 18, 23]
• 1945 – Promethium-147 (half-life 2.62 years) and promethium-149 (half-life 53 hours) were isolated from uranium fission products at Clinton Laboratories [3, 8, 13]
• 1947 – The Oak Ridge team announced their discovery of promethium, delayed from 1945 due to wartime secrecy and military research priorities [1, 3, 4, 13, 18]
• 1947 – Ion-exchange chromatography was used to firmly establish promethium’s identification [3, 6, 13]
• 1948 – The U.S. National Research Council examined discovery claims and recommended the name “promethium” to the Commission on Nomenclature for Inorganic Chemistry [24, 25]
• June 28, 1948 – Participants at an American Chemical Society symposium in Syracuse saw the first specimens of promethium compounds (yellow chloride and pink nitrate) [20]
• 1949 – The International Union of Pure and Applied Chemistry (IUPAC) officially accepted the name “promethium” with the spelling changed from the originally proposed “prometheum” [1, 10, 13, 24, 25]
• 1950 – The International Atomic Balance Commission confirmed the name “promethium” while rejecting previous names illinium, florentium, and cyclonium [6]
• 1963 – The first sample of promethium metal was prepared by reduction of promethium(III) fluoride with lithium in a tantalum crucible [1, 3, 11]
• 1970s – Oak Ridge National Laboratory’s rich inventory of promethium-147, obtained through traditional methods at Hanford, Washington, began to decline [6]
• May 22, 2024 – Scientists at Oak Ridge National Laboratory published the first observation of a promethium complex in solution in Nature, characterizing its coordination structure and bond length using X-ray absorption spectroscopy [26, 27, 28, 29, 30, 31, 32, 33, 34]
• 2024 – ORNL researchers discovered that promethium marks a key transition point in lanthanide contraction, where bond shortening accelerates through the first five rare earth elements then suddenly slows after promethium [26, 27, 31, 34]

Final Thoughts

The story of promethium reflects the evolution of chemistry itself, from theoretical predictions based on periodic trends to the sophisticated nuclear synthesis and spectroscopic techniques of today. Its discovery during the Manhattan Project exemplifies how wartime research can yield fundamental scientific knowledge, while its recent characterization at Oak Ridge National Laboratory demonstrates that even well-established elements can still hold secrets waiting to be unlocked. As the missing piece in understanding lanthanide contraction, promethium has proven essential to completing our picture of rare earth chemistry.

Looking forward, improved understanding of promethium’s properties may enable better separation techniques for all rare earth elements, potentially revolutionizing the production of these critical materials for modern technology. Like its mythological namesake who brought fire to humanity, promethium continues to illuminate new paths in nuclear science and materials chemistry, reminding us that there are still mysteries to be solved in even the most fundamental aspects of the periodic table.

Thanks for reading!

References

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[25] (PDF) IUPAC and the Naming of Elements – https://www.researchgate.net/publication/333810640_IUPAC_and_the_Naming_of_Elements

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