Common Types of Ionic Solids

Unlike metallic solids, however, ionic solids are unable to closest pack in the crystalline state for two different reasons. First, the sizes of the anions and the cations in an ionic solid are rarely the same. Second, and more importantly, because the ions have opposite charges, the lowest energy configuration is one that minimizes the repulsion of like charges and maximizes the attraction between ions of opposite charge. 

NaCI lattice. [Reproduced from http //en.wikipedia.org/wiki/Sodium chloride (accessed January I I, 2014).] 

Principles of Inorganic Chemistry, First Edition. Brian W. Pfennig. 

Halite (NaCI) unit cell in (a) ball and stick and (b) space-filling representations. 

The octahedrons surrounding the Ni ions in NiAs, on the other hand, are edge-shared in one direction while face-shared in another, leading to a layered structure with an ABABAB-type repeating motif. The following molecules all crystallize in the nickel arsenide structure TiS, TiSe, TiTe, CrS, CrSe, CrTe, CrSb, NiS, NiSe, NiTe, NiSb, and NiSn. 

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