Rock salt structure

The rock salt structure is a cubic crystal arrangement in which each ion has six nearest neighbors of opposite charge. Its two interpenetrating ion sublattices are offset by half a unit cell.

Coordination number: The number of nearest neighboring atoms or ions surrounding a particle in a crystal or molecule. Each ion in this structure has six nearest neighbors.
Sodium chloride: An ionic compound composed of sodium and chloride ions, commonly crystallizing in the rock salt structure. Its crystal is the standard example of this arrangement.
Potassium chloride: An ionic compound that forms crystals with the rock salt structure under ordinary conditions. It is another familiar alkali halide with this crystal arrangement.
Cesium chloride structure: A cubic ionic structure in which each ion has eight nearest neighbors of opposite charge. Its eightfold coordination distinguishes it from rock salt’s sixfold coordination.
Face-centered cubic: A cubic lattice with points at each cube corner and face center. Each ion species forms a face-centered cubic sublattice.
Lattice energy: The energy change associated with forming an ionic crystal from separated gaseous ions. It quantifies the energetic contribution of the arrangement’s electrostatic interactions.
Magnesium oxide: An ionic compound of magnesium and oxygen that crystallizes in the rock salt structure. Its divalent ions show that the arrangement is not limited to singly charged ions.
Fluorite structure: A cubic structure exemplified by calcium fluoride, with cations eightfold and anions fourfold coordinated. Its unequal coordination numbers contrast with the sixfold coordination of both ion types here.
Unit cell: The smallest repeating volume that represents a crystal’s translational structure. A rock salt crystal can be described by a cubic repeating cell.
Madelung constant: A dimensionless factor that sums electrostatic interactions across an ionic crystal’s lattice. Its value depends on the rock salt geometry and enters lattice-energy calculations.

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