The alkali metals consist of the chemical elements lithium (Li), sodium (Na), potassium (K), rubidium (Rb), caesium (Cs), and francium (Fr). Together with hydrogen they constitute group 1, which lies in the s-block of the periodic table. All alkali metals have their outermost electron in an s-orbital: this shared electron configuration results in their having very similar characteristic properties. Indeed, the alkali metals provide the best example of group trends in properties in the periodic table, with elements exhibiting well-characterised homologous behaviour. This family of elements is also known as the lithium family after its leading element.
Caesium is a chemical element with the symbol Cs and atomic number 55. It is a soft, silvery-golden alkali metal with a melting point of 28.5 °C (83.3 °F), which makes it one of only five elemental metals that are liquid at or near room temperature. Caesium has physical and chemical properties similar to those of rubidium and potassium. It is pyrophoric and reacts with water even at −116 °C (−177 °F). It is the least electronegative element, with a value of 0.79 on the Pauling scale. It has only one stable isotope, caesium-133. Caesium is mined mostly from pollucite. Caesium-137, a fission product, is extracted from waste produced by nuclear reactors. It has the largest atomic radius of all elements whose radii have been measured or calculated, at about 260 picometers.
Caesium fluoride or cesium fluoride is an inorganic compound with the formula CsF and it is a hygroscopic white salt. Caesium fluoride can be used in organic synthesis as a source of the fluoride anion. Caesium also has the highest electropositivity of all known elements and fluorine has the highest electronegativity of all known elements.
Caesium hydroxide is a strong base containing the highly reactive alkali metal caesium, much like the other alkali metal hydroxides such as sodium hydroxide and potassium hydroxide. It is the strongest of the five alkali metal hydroxides. Fused Caesium hydroxide dissolves glass by attacking silica framework and it has applications in bringing glass samples into a solution for analytical purposes in commercial glass industry and defense waste processing facility. The melting process is carried out in a nickel or zirconium crucible. Cesium hydroxide fusion at 750°C produces complete dissolution of glass pellets.
Caesium iodide or cesium iodide is the ionic compound of caesium and iodine. It is often used as the input phosphor of an X-ray image intensifier tube found in fluoroscopy equipment. Caesium iodide photocathodes are highly efficient at extreme ultraviolet wavelengths.
Caesium chloride or cesium chloride is the inorganic compound with the formula CsCl. This colorless salt is an important source of caesium ions in a variety of niche applications. Its crystal structure forms a major structural type where each caesium ion is coordinated by 8 chloride ions. Caesium chloride dissolves in water. CsCl changes to NaCl structure on heating. Caesium chloride occurs naturally as impurities in carnallite, sylvite and kainite. Less than 20 tonnes of CsCl is produced annually worldwide, mostly from a caesium-bearing mineral pollucite.
Tungstic acid refers to hydrated forms of tungsten trioxide, WO3. Both a monohydrate (WO3·H2O) and hemihydrate (WO3·1/2 H2O) are known. Molecular species akin to sulfuric acid, i.e. (HO)2WO2 are not observed.
Caesium acetate or cesium acetate is an ionic caesium compound with the molecular formula CH3COOCs. It is a white solid that may be formed by the reaction of caesium hydroxide or caesium carbonate with acetic acid.
Caesium chromate or cesium chromate is an inorganic compound with the formula Cs2CrO4. It is a yellow crystalline solid that is the caesium salt of chromic acid, and it crystallises in the orthorhombic system.
Caesium carbonate or cesium carbonate is a white crystalline solid compound. Caesium carbonate has a high solubility in polar solvents such as water, alcohol and DMF. Its solubility is higher in organic solvents compared to other carbonates like potassium and sodium carbonates, although it remains quite insoluble in other organic solvents such as toluene, p-xylene, and chlorobenzene. This compound is used in organic synthesis as a base. It also appears to have applications in energy conversion.
Caesium bromide or cesium bromide is an ionic compound of caesium and bromine with the chemical formula CsBr. It is a white or transparent solid with melting point at 636 °C that readily dissolves in water. Its bulk crystals have the cubic CsCl structure, but the structure changes to the rocksalt type in nanometer-thin film grown on mica, LiF, KBr or NaCl substrates.
Caesium cadmium chloride (CsCdCl3) is a synthetic crystalline material. It belongs to the AMX3 group (where A=alkali metal, M=bivalent metal, X=halogen ions). It crystallizes in a hexagonal space group P63/mmc with unit cell lengths a = 7.403 Å and c = 18.406 Å, with one cadmium ion having D3d symmetry and the other having C3v symmetry.
Caesium sulfate or cesium sulfate is the inorganic compound and salt with the formula Cs2SO4. It is a white water-soluble solid that is used to prepare dense aqueous solutions for use in isopycnic (or "density-gradient") centrifugation. It is isostructural with potassium salt.
Zirconium perchlorate is a molecular substance containing zirconium and perchlorate groups with formula Zr(ClO4)4. Zr(ClO4)4 is a volatile crystalline product. It can be formed by reacting zirconium tetrachloride with dry perchloric acid at liquid nitrogen temperatures. Zr(ClO4)4 sublimes slowly in a vacuum at 70°C showing that the molecule is covalently bound rather than being ionic. The reaction also forms some zirconyl perchlorate (or zirconium oxyperchlorate) ZrO(ClO4)2 as even apparently pure perchloric acid is in equilibrium with dichlorine heptoxide, hydronium ions and perchlorate ions. This side product can be minimised by adding more dichlorine heptoxide or doing the reaction as cold as possible.
Caesium oxalate (standard IUPAC spelling) dicesium oxalate, or cesium oxalate (American spelling) is the oxalate of caesium. Caesium oxalate has the chemical formula of Cs2C2O4.
Caesium peroxide or cesium peroxide is a compound of caesium and oxygen. It can be formed from caesium metal by adding a stoichiometric amount in ammonia solution, or oxidizing the solid metal directly.
Caesium ozonide (CsO3) is an oxygen-rich compound of caesium. It is an ozonide, meaning it contains the ozonide anion (O3−). It can be formed by reacting ozone with caesium superoxide:
Caesium superoxide is the superoxide of caesium. It is an orange solid.
Caesium enneabromodibismuthate is an inorganic compound with the formula Cs3Bi2Br9. It is one of the coordination complexes formed by caesium, bismuth and bromine. At room temperature, it is trigonal (P3m1) and it undergoes phase transformation to monoclinic phase (C12/c1) when the temperature is below 96 K.
Caesium triiodide is an inorganic compound, with the chemical formula of CsI3. It can be prepared by slow volatilization and crystallization of caesium iodide and iodine in aqueous ethanol solution. It can form precipitates with diazobenzene.
