Francium compounds are compounds containing the element

francium Francium is a chemical element with the symbol Fr and atomic number 87. It is extremely radioactive; its most stable isotope, francium-223 (originally called actinium K after the natural decay chain it appears in), has a half-life of only 22&nb ...

(Fr). Due to francium being very unstable, its salts are only known to a small extent. Francium coprecipitates with several caesium salts, such as

caesium perchlorate Caesium perchlorate or cesium perchlorate (CsClO4), is a perchlorate of caesium. It forms white crystals, which are sparingly soluble in cold water and ethanol. It dissolves more easily in hot water. CsClO4 is the second least soluble of the alk ...

, which results in small amounts of francium perchlorate. This coprecipitation can be used to isolate francium, by adapting the radiocaesium coprecipitation method of

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and C. M. Nelson. It will additionally coprecipitate with many other caesium salts, including the iodate, the picrate, the tartrate (also

rubidium Rubidium is the chemical element with the symbol Rb and atomic number 37. It is a very soft, whitish-grey solid in the alkali metal group, similar to potassium and caesium. Rubidium is the first alkali metal in the group to have a density higher ...

tartrate), the chloroplatinate, and the

silicotungstate Silicotungstic acid or tungstosilicic acid is a heteropoly acid with the chemical formula . It forms hydrates . In freshly prepared samples, ''n'' is approximately 29, but after prolonged desiccation, ''n'' = 6. It is a white solid although impu ...

. It also coprecipitates with

silicotungstic acid Silicotungstic acid or tungstosilicic acid is a heteropoly acid with the chemical formula . It forms hydrates . In freshly prepared samples, ''n'' is approximately 29, but after prolonged desiccation, ''n'' = 6. It is a white solid although impur ...

, and with

perchloric acid Perchloric acid is a mineral acid with the formula H Cl O4. Usually found as an aqueous solution, this colorless compound is a stronger acid than sulfuric acid, nitric acid and hydrochloric acid. It is a powerful oxidizer when hot, but aqueous sol ...

, without another alkali metal as a

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, which leads to other methods of separation.E. N K. Hyde ''Radiochemistry of Francium'', Subcommittee on Radiochemistry, National Academy of Sciences-National Research Council; available from the Office of Technical Services, Dept. of Commerce, 1960.

Halides

Francium halides are all soluble in water and are expected to be white solids. They are expected to be produced by the reaction of the corresponding

halogen The halogens () are a group in the periodic table consisting of five or six chemically related elements: fluorine (F), chlorine (Cl), bromine (Br), iodine (I), astatine (At), and tennessine (Ts). In the modern IUPAC nomenclature, this group is ...

s. For example, francium chloride would be produced by the reaction of francium and

chlorine Chlorine is a chemical element with the Symbol (chemistry), symbol Cl and atomic number 17. The second-lightest of the halogens, it appears between fluorine and bromine in the periodic table and its properties are mostly intermediate betwee ...

. Francium chloride has been studied as a pathway to separate francium from other elements, by using the high vapour pressure of the compound, although francium fluoride would have a higher vapour pressure.

Other compounds

Francium nitrate, sulfate, hydroxide, carbonate, acetate, and oxalate, are all soluble in water, while the iodate, picrate, tartrate, chloroplatinate, and

are insoluble. The insolubility of these compounds are used to extract francium from other radioactive products, such as

zirconium Zirconium is a chemical element with the symbol Zr and atomic number 40. The name ''zirconium'' is taken from the name of the mineral zircon, the most important source of zirconium. The word is related to Persian '' zargun'' (zircon; ''zar-gun'', ...

niobium Niobium is a chemical element with chemical symbol Nb (formerly columbium, Cb) and atomic number 41. It is a light grey, crystalline, and ductile transition metal. Pure niobium has a Mohs hardness rating similar to pure titanium, and it has sim ...

molybdenum Molybdenum is a chemical element with the symbol Mo and atomic number 42 which is located in period 5 and group 6. The name is from Neo-Latin ''molybdaenum'', which is based on Ancient Greek ', meaning lead, since its ores were confused with lea ...

tin Tin is a chemical element with the symbol Sn (from la, stannum) and atomic number 50. Tin is a silvery-coloured metal. Tin is soft enough to be cut with little force and a bar of tin can be bent by hand with little effort. When bent, t ...

antimony Antimony is a chemical element with the symbol Sb (from la, stibium) and atomic number 51. A lustrous gray metalloid, it is found in nature mainly as the sulfide mineral stibnite (Sb2S3). Antimony compounds have been known since ancient time ...

, the method mentioned in the section above. The CsFr molecule is predicted to have francium at the negative end of the dipole, unlike all known heterodiatomic alkali metal molecules. Francium superoxide (FrO₂) is expected to have a more

covalent A covalent bond is a chemical bond that involves the sharing of electrons to form electron pairs between atoms. These electron pairs are known as shared pairs or bonding pairs. The stable balance of attractive and repulsive forces between atoms ...

character than its lighter congeners; this is attributed to the 6p electrons in francium being more involved in the francium–oxygen bonding. The relativistic destabilisation of the 6p_3/2 spinor may make francium compounds in oxidation states higher than +1 possible, such as r^VF₆sup>−; but this has not been experimentally confirmed. Francium perchlorate is produced by the reaction of francium chloride and

sodium perchlorate Sodium perchlorate is the inorganic compound with the chemical formula Na ClO4. It is a white crystalline, hygroscopic solid that is highly soluble in water and in alcohol. It is usually encountered as the monohydrate. The compound is noteworthy ...

. The francium perchlorate coprecipitates with

. This coprecipitation can be used to isolate francium, by adapting the radiocaesium coprecipitation method of

and C. M. Nelson. However, this method is unreliable in separating

thallium Thallium is a chemical element with the Symbol (chemistry), symbol Tl and atomic number 81. It is a gray post-transition metal that is not found free in nature. When isolated, thallium resembles tin, but discolors when exposed to air. Chemists W ...

, which also coprecipitates with caesium. Francium perchlorate's

entropy Entropy is a scientific concept, as well as a measurable physical property, that is most commonly associated with a state of disorder, randomness, or uncertainty. The term and the concept are used in diverse fields, from classical thermodynam ...

is expected to be 42.7 e.u (178.7 J mol⁻¹ K⁻¹). The only double salt known of francium has the formula Fr₉Bi₂I₉.

References

{{reflist Compounds Chemical compounds by element

Halides

Other compounds

See also

References