Non-stoichiometric compounds
While “classic” molecules are understood by stoichiometric compounds , unstoichiometric compounds cannot be viewed as molecules in the actual sense. Such compounds are often crystalline phases of changing composition such as isomorphic compounds ( isomorphism ), intercalation mixed crystals with interstitial atoms , substitution mixed crystals (exchange of atoms in the crystal lattice), semiconductors .
In chemical notation, the lack of stoichiometry is expressed by variables: for example Cu x Ni 1 − x
Non-stoichiometry is particularly widespread for substances with metal or secondary valence bonds ( chemical bonds ) and especially for chalcogenides , metal hydrides , borides , carbides , silicides and phosphides , inclusion compounds , solid solutions of gases in metals, when Crystal defects , mixed crystals and alloys as well as compounds that additionally absorb variable amounts of another metal (such as tungsten bronzes M x WO 3 , with M = alkali metal , Cu, Ag, Ti or Pb) are often found.
literature
- Paul Nylén, Nils Wigren, Günter Joppien: Introduction to stoichiometry . Steinkopff Verlag Darmstadt, 19th edition 1995 ( limited preview in the Google book search), p. 30.
- Norman N. Greenwood: Ionic Crystals, Lattice Defects, and Non-Stoichiometric Compounds . Verlag Chemie, Weinheim, 1973, ISBN 978-3-527-25433-0 .