Madelung Constants(A

) for Common Crystal Lattices*

Sodium chloride 1.75
Cesium chloride 1.76
Zinc blende 1.64
Wurtzite 1.64
Fluorite 5.04
Rutile 4.82**
Corundum 25.03**

* The Madelung constant, A, is used in the equation E = AZ 2e 2/r, where r is the sum of the ionic radii, e is the charge on an electron, and Z is the highest common denominator of the absolute values of the integral charges on the ions (e.g., for MgCl2, Z = 1; for CaO, Z = 2).
** Depends on exact structure.

Reference: Huheey, pps. 99-134.