Chemical Education Today
Commentary
My Favorite Element Francium: Uranium’s Daughter, Perey’s Discovery Mary Virginia Orna Chemistry Department, College of New Rochelle, New Rochelle, NY 10805;
[email protected] When I recently accessed The Periodic Table of Videos (1) and clicked on francium, element number 87, the narrator said that the element had been discovered by one of Marie Curie’s assistants. It distressed me that he did not mention whom, and it further distressed me that this person was called an assistant when she was a research technician in her own right by the time the element was discovered—and Marie Curie had been dead for five years. The discoverer, of course, was Marguerite Perey, one of not even a full handful of women who have discovered elements in their own right—and Perey’s discovery should be celebrated, not ignored. That is why francium is my favorite element. You will not find francium on a list of elements for sale in a chemical catalog—nor can you even expect to find it among the more exotic elements with very low natural abundances. Francium’s most long-lived isotope, Fr-223, has a half-life of a mere 22 minutes. It is estimated to exist in the sun at around 8 ppb; a quick, back-of-the-envelope calculation based upon the annual production of uranium (francium is the fourth daughter in the U-235 decay series), assuming secular equilibrium, yields an estimated 1.2 × 10-11 grams of this elusive element in the combined worldwide uranium production bins. This is certainly not the amount that Perey had at her disposal while searching for the proverbial needle in—probably 20 million haystacks! She found the “needle” by painstakingly carrying out hundreds of fractional crystallizations and then quickly and skillfully analyzing each fraction. Her discovery was not an accident. In addition to its discovery by a woman, francium has always fascinated me as the element at the very bottom left of the s-block in the periodic table, and therefore expected to be the most electropositive element with an estimated Pauling electronegativity of 0.7. Combine francium with fluorine, the most electronegative element (EN = 4.0), and you should get the most stable alkali halide, FrF, with an electronegativity difference of 3.3—if you could ever find enough francium to do so. While this short piece has the element as its centerpiece, its discoverer also makes for fascinating reading. The first woman to be elected to the Académie des Sciences (French Academy of Sciences), professor and chair of the department of nuclear chemistry at the University of Strasbourg, and laden with many honors, she succumbed at the age of 65 to cancer contracted through her research. I have listed the references to Perey’s papers on her most famous discovery as well as a reference to a brief article on her life and her work (2–5). An article that examines the chemistry of astatine and francium has appeared in this Journal (6).
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Marguerite Perey. Photograph courtesy of AIP Emilio Segrè Visual Archives—gift of J. D. Adloff. Reprinted with permission.
Literature Cited 1. The Periodic Table of Videos, from the University of Nottingham, is at http://www.periodicvideos.com/ (accessed Oct 2009). 2. Kauffman, G. B.; Adloff, J.-P. Marguerite Catherine Perey (1909–1975). In Women in Chemistry and Physics: A Biobibliographic Sourcebook, Grinstein, L. S., Rose, R. K., Rafailovich, M. H., Eds.; Greenwood Press: Westport, CT and London, 1993; pp 470–475. 3. Perey, M. Sur un Élément 87, Dérivé de l’Actinium. ComptesRendus Hebdomadaires des Séances de l’Académie des Sciences 1939, 208, 97. 4. Perey, M. Francium: Élément 87. Bulletin de la Société Chimique de France 1951, 18, 779. 5. Perey, M. On the Descendants of Actinium K: 87Ac223. Journal de Physique et le Radium 1956, 17, 545. 6. Hyde, E. K. Astatine and Francium. J. Chem. Educ. 1959, 36, 15–21.
Supporting JCE Online Material
http://www.jce.divched.org/Journal/Issues/2009/Dec/abs1364.html Abstract and keywords Full text (PDF) with links to cited URLs and JCE article
Journal of Chemical Education • Vol. 86 No. 12 December 2009 • www.JCE.DivCHED.org • © Division of Chemical Education
