Francium, (the element that took its name from the country, France) was discovered by Marguerite Perey in France in 1939. She had discovered an element, while analyzing actinium’s decay sequence and named francium, in honour of her country. It was the last element that discovered in nature first, rather than by synthesis. All elements discovered since then have been discovered when the element has been synthesized in the laboratory. Its discovery completed humankind’s discoveries of naturally occurring elements.
Marguerite Perey (who discovered francium) in Lab
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Properties
Physical Properties
It is a chemical element with the symbol ‘Fr’ and atomic number 87. Before its discovery, it was referred to as Eka-caesium. It is the heaviest chemical element in group-1 of the periodic table, alkali metal group. It is one of the most unstable of the naturally occurring element. It is extremely radioactive; its most stable isotope francium-223 has a half-life of only 22 minutes. The isotopes of francium quickly decay into astatine, radium, and radon. It is a heavy element with a single valence electron and has the highest equivalent weight of any element. Francium’s melting point was estimated to be around 8.0 °C. This is uncertain because of the element’s extreme rarity and radioactivity. The density of francium is expected to be around 2.48 g/cm3.
Chemical Properties
Francium is an alkali metal whose chemical properties mostly resemble those of caesium. Francium has slightly higher ionization energy than caesium, also it should have higher electron affinity than caesium. The CsFr molecule is predicted to have francium at the negative end of the dipole, unlike all known heteroatomic alkali metal molecules. 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. Additionally, it will coprecipitate with many other caesium salts including the iodate, the picrate, the tartrate (also rubidium tartrate), the chloroplatinate, and the silicotungstate. Nearly all francium salts are water-soluble.
Isotopes
There are 34 known isotopes of francium ranging in atomic mass from 199 to 232. Francium-223 and francium-221 are the only isotopes that occur in nature. Francium-223 is the most stable isotope with a half-life of 21.8 minutes and it is highly unlikely that an isotope of francium with a longer half-life will ever be discovered or synthesized. Francium-223 decays into radium-223 by beta decay, with minor alpha decay to astatine-219. Francium-221 has a half-life of 4.8 minutes. It then decays into astatine-217 by alpha decay. The least stable ground state isotope is francium-215, with a half-life of 0.12 μs.
Francium-223 stable isotope
Uses
There are no commercial applications for francium, due to its instability and rarity. However, the few of its uses are described as follows:
For Research Purposes
It has been used for research purposes in the field of chemistry. Its ability to be synthesized, trapped, and cooled, along with its relatively simple atomic structure, has made it the subject of specialized spectroscopy experiments. These experiments have led to more specific information regarding energy levels and the coupling constants between subatomic particles. 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.
Francium in the Research field
Diagnosis for Cancer
It has been explored as a potential diagnostic aid for various cancers; although, this application has been deemed impractical.
Francium in Cancer Diagnosis