Francium

melting point: 27°C
boiling point: 677°C
density: unknown
most common ion: Fr ⁺

The element francium is named for the country of France and its most stable isotope is known as actinium K. Dimitri Mendeleev assigned it the name eka-cesium prior to its actual discovery, although at this time it was also known as russium, virginium, and moldavium. Marguerite Perey, a one-time assistant of Marie Curie, discovered francium in 1939. It is not found in its elemental state and less than one ounce is thought to exist in Earth's crust at any one time.

Although there are a number of isotopes of francium, most decay very rapidly to other elements. Most isotopes with masses of 223 AMU and lower emit α -particles (consisting of two protons and two neutrons) to become astatine. Some low mass francium isotopes can also undergo electron capture (the conversion of a proton to a neutron through the absorption of an electron) to become radon. Francium isotopes with masses of 220 AMU and higher can undergo β -decay (the conversion of a neutron to a proton through the emission of an electron) to become radium. Francium-223 is the most stable isotope and has a half-life of 21.8 minutes.

Naturally occurring francium is the product of a side reaction of the decay pathway of actinium. Actinium-227 generally undergoes β -decay to produce thorium-227, but about 1 percent of the actinium emits an α -particle to form francium-223. Francium can be produced in the laboratory via proton bombardment of thorium and during oxygen 18 (O-18) bombardment of heated gold.

Because of its extremely low abundance, short half-life, and high radioactivity, neither francium nor its compounds have economic applications.

see also Alkali Metals; Curie, Marie Sklodowska; Mendeleev, Dimitri; Radioactivity.

Nathan J. Barrows

Bibliography

Heiserman, David L. (1992). Exploring Chemical Elements and Their Compounds. Blue Ridge Summit, PA: Tab Books.

Lide, David R., ed. (2000). CRC Handbook of Chemistry & Physics, 81st edition. New York: CRC Press.

francium [from France ], radioactive chemical element; symbol Fr; at. no. 87; mass no. of most stable isotope 223; m.p. about 27°C (estimated); b.p. 677°C (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.

francium (symbol Fr) Radioactive metallic element, discovered ((1939) by French physicist Marguerite Perey (1909–75). It occurs naturally in uranium ores and is a decay product of actinium. Properties: at.no. 87; most stable isotope Fr²²³ (half life 22 minutes).

fran·ci·um / ˈfransēəm/ • n. the chemical element of atomic number 87, a radioactive member of the alkali metal group. Francium occurs naturally as a decay product in uranium and thorium ores. (Symbol: Fr)

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