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; it has 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.
This is a list of common chemical compounds with chemical formulae and CAS numbers, indexed by formula. This complements alternative listing at list of inorganic compounds. There is no complete list of chemical compounds since by nature the list would be infinite.
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.
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 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 hydride or cesium hydride is an inorganic compound of caesium and hydrogen with the chemical formula CsH. It is an alkali metal hydride. It was the first substance to be created by light-induced particle formation in metal vapor, and showed promise in early studies of an ion propulsion system using caesium. It is the most reactive stable alkaline metal hydride of all. It is a powerful superbase and reacts with water extremely vigorously.
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.
Caesium tungstate or cesium tungstate is an inorganic chemical compound that is notable for forming a very dense liquid in solution. The solution is used in diamond processing, since diamond sinks in it, whereas most other rocks float.
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 azide or cesium azide is an inorganic compound of caesium and nitrogen. It is a salt of azide with the formula CsN3.
Caesium peroxide or cesium peroxide is an inorganic compound of caesium and oxygen with the chemical formula Cs2O2. It can be formed from caesium metal by adding a stoichiometric amount in ammonia solution, or oxidizing the solid metal directly.
Caesium oxide, or cesium oxide, describes inorganic compounds composed of caesium and oxygen. Several binary oxides of caesium are known.
Caesium ozonide is an oxygen-rich chemical compound of caesium, with the chemical formula CsO3. It consists of caesium cations Cs+ and ozonide anions O−3. It can be formed by reacting ozone with caesium superoxide:
Caesium sesquioxide is a chemical compound with the formula Cs2O3 or more accurately Cs4O6. It is an oxide of caesium containing oxygen in different oxidation states. It consists of caesium cations Cs+, superoxide anions O−2 and peroxide anions O2−2. Caesium in this compound has an oxidation state of +1, while oxygen in superoxide has an oxidation state of −1/2 and oxygen in peroxide has an oxidation state of −1. This compound has a structural formula of (Cs+)4(O−2)2(O2−2). Compared to the other caesium oxides, this phase is less well studied, but has been long present in the literature. It can be created by thermal decomposition of caesium superoxide at 290 °C.
Caesium superoxide is a chemical compound with the chemical formula CsO2. It consists of caesium cations Cs+ and superoxide anions O−2. It is an orange solid.
Caesium telluride or Caesium telluridocaesium is an inorganic salt with a chemical formula Cs2Te. Caesium telluride is used to make photo cathodes.
Caesium selenide is an inorganic compound of caesium and selenium. It is a selenide, with the chemical formula of Cs2Se. It can be prepared by reacting caesium and selenium. It has an inverse fluorite structure, with space group . There are 4 units per unit cell, and the other selenides from the same group are similar.
