Alkali metal halides, oralkali halides, are the family ofinorganic compounds with thechemical formula MX, where M is analkali metal and X is ahalogen. These compounds are the often commercially significant sources of these metals and halides. The best known of these compounds issodium chloride,table salt.[1]
Most alkali metal halides crystallize with theface-centered cubic lattices. In this structure both the metals and halides featureoctahedral coordination geometry, in which each ion has acoordination number of six. Caesium chloride, bromide, and iodide crystallize in abody-centered cubic lattice that accommodates coordination number of eight for the larger metal cation (and the anion also).[2]
The alkali metal halides exist as colourlesscrystalline solids, although as finely ground powders appear white. They melt at high temperature, usually several hundred degrees to colorless liquids. Their high melting point reflects their highlattice energies. At still higher temperatures, these liquids evaporate to give gases composed of diatomic molecules.
These compounds dissolve in polar solvents to give ionic solutions that contain highly solvated anions and cations. Alkali halides dissolve large amounts of the corresponding alkali metal: caesium is completely miscible at all temperatures above the melting point.[3]
The table below provides links to each of the individual articles for these compounds. The numbers beside the compounds show the electronegativity difference between the elements based on thePauling scale. The higher the number is, the more ionic the solid is.
| Alkali metals | |||||||
|---|---|---|---|---|---|---|---|
| Lithium | Sodium | Potassium | Rubidium | Caesium | |||
Halogens | Fluorine | LiF (3.0) | NaF (3.1) | KF (3.2) | RbF (3.2) | CsF (3.3) | |
| Chlorine | LiCl (2.0) | NaCl (2.1) | KCl (2.2) | RbCl (2.2) | CsCl (2.3) | ||
| Bromine | LiBr (1.8) | NaBr (1.9) | KBr (2.0) | RbBr (2.0) | CsBr (2.1) | ||
| Iodine | LiI (1.5) | NaI (1.6) | KI (1.7) | RbI (1.7) | CsI (1.8) | ||