AskDefine | Define francium

Dictionary Definition

francium n : a radioactive element of the alkali-metal group discovered as a disintegration product of actinium [syn: Fr, atomic number 87]

User Contributed Dictionary

see Francium

English

Etymology

francium, named after the native country of Marguerite Perey: France (see also gallium).

Noun

  1. A metallic chemical element (symbol Fr) with an atomic number of 87.

Synonyms

Derived terms

Translations

External links

  • elements.vanderkrogt.net – more information about the etymology and the chemical element. (Some of the translations were taken from that site with the permission of the author.)

Extensive Definition

Francium (), formerly known as eka-caesium and actinium K, is a chemical element that has the symbol Fr and atomic number 87. It has the lowest known electronegativity of all known elements, and is the second rarest naturally occurring element (after astatine). Francium is a highly radioactive metal that decays into astatine, radium, and radon. As an alkali metal, it has one valence electron.
Francium was discovered by Marguerite Perey in France (from which the element takes its name) in 1939. It was the last element discovered in nature, rather than synthesized. Outside the laboratory, francium is extremely rare, with trace amounts found in uranium and thorium ores, where the isotope francium-223 continually forms and decays. As little as 30 g (one ounce) exists at any given time throughout the Earth's crust; the other isotopes are entirely synthetic. The largest amount ever collected of any isotope was a cluster of 10,000 atoms (of francium-210) created as an ultracold gas at Stony Brook in 1997.

Characteristics

Francium is less stable than any other element lighter than element 106, seaborgium:
Francium is an alkali metal whose chemical properties most resemble those of caesium. it has the highest equivalent weight of any element. caesium has the second-lowest at 0.79. Liquid francium — if such a substance were to be created — should have a surface tension of 0.05092 N/m at its melting point. Francium coprecipitates with several caesium salts, such as caesium perchlorate, which results in small amounts of francium perchlorate. This coprecipitation can be used to isolate francium, by adapting the radiocaesium coprecipitation method of Glendenin and Nelson. It will additionally coprecipitate with many other caesium salts, including the iodate, the picrate, the tartrate (also rubidium tartrate), the chloroplatinate, and the silicotungstate. It also coprecipitates with silicotungstic acid, and with perchloric acid, without another alkali metal as a carrier, which provides other methods of separation. Nearly all francium salts are water-soluble.

Applications

Due to its instability and rarity Studies on the light emitted by laser-trapped francium-210 ions have provided accurate data on transitions between atomic energy levels which are fairly similar to those predicted by quantum theory.

History

As early as 1870, chemists thought that there should be an alkali metal beyond caesium, with an atomic number of 87. Research teams attempted to locate and isolate this missing element, and at least four false claims were made that the element had been found before an authentic discovery was made.

Erroneous and incomplete discoveries

Russian chemist D. K. Dobroserdov was the first scientist to claim to have found eka-caesium, or francium. In 1925, he observed weak radioactivity in a sample of potassium, another alkali metal, and concluded that eka-caesium was contaminating the sample. He then published a thesis on his predictions of the properties of eka-caesium, in which he named the element russium after his home country. Shortly thereafter, Dobroserdov began to focus on his teaching career at the Polytechnic Institute of Odessa, and he did not pursue the element further. In 1934, however, H.G. MacPherson of UC Berkeley disproved the effectiveness of Allison's device and the validity of this false discovery.
In 1936, Romanian chemist Horia Hulubei and his French colleague Yvette Cauchois also analyzed pollucite, this time using their high-resolution X-ray apparatus. Francium was the last naturally occurring element to be discovered, following rhenium in 1925.

Occurrence

Natural

Francium-223 is the result of the alpha decay of actinium-227 and can be found in trace amounts in uranium and thorium minerals. This makes it the second rarest element in the crust after astatine. which are then isolated by the magneto-optic trap (MOT). Other synthesis methods include bombarding radium with neutrons, and bombarding thorium with protons, deuterons, or helium ions. Francium has not yet, as of 2006, been synthesized in amounts large enough to weigh.

Isotopes

There are 34 known isotopes of francium ranging in atomic mass from 199 to 232. Francium has seven metastable nuclear isomers.
Francium-223 is the most stable isotope with a half-life of 21.8 minutes, Francium-223 then decays into radium-223 by beta decay (1149 keV decay energy), with a minor (0.006%) alpha decay path to astatine-219 (5.4 MeV decay energy).
Francium-221 has a half-life of 4.8 minutes.
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francium in Lithuanian: Francis
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francium in Polish: Frans (pierwiastek)
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francium in Simple English: Francium
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