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Relations Between Normal Boiling Point and Melting Point for Simple Halides and Oxides
Author(s) -
UITERT L. G.
Publication year - 1983
Publication title -
journal of the american ceramic society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.9
H-Index - 196
eISSN - 1551-2916
pISSN - 0002-7820
DOI - 10.1111/j.1151-2916.1983.tb10054.x
Subject(s) - chemistry , halide , valence electron , crystallography , melting point , ion , electron , valence (chemistry) , metal , boiling point , halogen , inorganic chemistry , alkyl , physics , organic chemistry , quantum mechanics
For most halides the normal boiling point ( T b in kelvin units) is given by the relation: T b = 440 n c ( ip·ea·d 2 ) −1 , where n c is the coordination number of the cation, ip the first ionization potential of the metal (in electron volts), ea the electron affinity of the anion former (in electron volts), and d the bond length in the crystal (in nanometers). Similar relations are found for oxides. For both classes the following relation applies: T b /T f = 1 + 0.67 /V a , where TI is the melting point of the crystal and V a is the valence of the anion. Exceptions occur when inert ( s 2 ) electron pairs form the outer shield of the cation or anion core, when electron spin pairing occurs between halogen or oxygen atoms, when there are direct interactions between metal atoms, or when n c is not the same in the molten and crystalline states. Further, it is shown that covalency related to the asymmetric polarization of anions by cations with partially filled valence shells can markedly increase cohesion in the melt. This relates to plasticity in the solid as well.