The Alkaline-Earth Oxides, Sulfides, Selenides, and Tellurides

The Alkaline-Earth Oxides, Sulfides, Selenides, and Tellurides.— 

Tabus 13-12.—Intebionic Distances in Crystals M++X— with the Sodium Chloride Arrangement 

In magnesium sulfide and selenide the anions are in contact the radii deduced on this assumption (1.80 A for S—, 1.93 A for Se—) are slightly smaller than the crystal radii. The ratio AW1- / o is 0.46, 

Crystals with the Rutile and the.Fluorite Structures Interionic Distances for Substances of Unsymmetrical Valence Type.—In a crystal of a substance of unsymmetrical valence type, such as fluorite, CaFs (Fig. 13-10), the equilibrium cation-anion interionic distance cannot be expected necessarily to be given by the sum of the crystal radii of the bivalent calcium ion and the univalent fluoride ion. The sum of the univalent radii of calcium and fluoride, 2.54 A, would give the equilibrium interionic distance in a hypothetical crystal with attractive and repulsive forces corresponding to the sodium chloride arrangement. 

According to Equation 13-3 the ratio of equilibrium distances for the two structures is 

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The Alkaline-Earth Oxides, etc.—The observed and calculated inter-atomic distances for the alkaline-earth oxides, sulfides, selenides and tellurides are given in Table VIII. Except for the magnesium com-... 

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