Alkali metal halide
Alkali metal halides are the family of inorganic compounds with the chemical formula MX, where M is an alkali metal and X is a halogen. These compounds are the often commercially significant sources of these metals and halides. The best known of these compounds is sodium chloride, table salt.
Structure
Most alkali metal halides crystallize with the face centered cubic lattices. In this structure both the metals and halides feature octahedral coordination geometry. The cesium halides crystallizes in a centered cubic motif that accommodates higher coordination number for the metal cation.[1]
Properties
The alkali metal halides exist as colourless crystalline 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 high lattice 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.
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 the Pauling scale. The higher the number is, the more ionic is the solid.
| Alkali Metals | |||||||
|---|---|---|---|---|---|---|---|
| Lithium | Sodium | Potassium | Rubidium | Caesium | |||
| H a l o g e n s |
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) | ||
References
- ^ Greenwood, N. N.; & Earnshaw, A. (1997). Chemistry of the Elements (2nd Edn.), Oxford:Butterworth-Heinemann. ISBN 0-7506-3365-4.
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