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Definition: francium from The Penguin Dictionary of Science

Symbol Fr. The element with atomic number 87 and most stable isotope 223, which is the alkali metal with the largest atomic number. Its chemistry is dominated by its radioactivity. The expected single oxidation number of +1 has been confirmed, although no common compounds exist in nature.


Summary Article: francium from The Columbia Encyclopedia

(frăn'sēəm) [from France], radioactive chemical element; symbol Fr; at. no. 87; mass no. of most stable isotope 223; m.p. about 27 degrees Celsius (estimated); b.p. 677 degrees Celsius (estimated); sp. gr. unknown; valence +1. Francium is extremely rare; its most stable isotope (half-life about 22 minutes) occurs naturally, to a very limited extent, in uranium minerals. More than 30 other isotopes of francium are known; some are prepared by bombarding thorium with protons, deuterons, or alpha particles.

Francium is one of the alkali metals found in Group 1 of the periodic table. Because it is so rare, its chemical and physical properties are not known, but it is believed to resemble cesium. The element was discovered in 1939 by Marguerite Perey at the Curie Institute in Paris as a product of the radioactive disintegration of actinium. In the United States it was at one time called virginium.

The Columbia Encyclopedia, © Columbia University Press 2017

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