Ionic Radii:
     Cs⁺, 169 pm
     Cl ^-, 181 pm
Radius Ratio: = 169/181 = 0.933

The radius ratio is such that we expect the cesium ions to occupy cubic holes in an array of chloride ions.

The stoichiometry (one Cs⁺ ion per each Cl ^- ion) requires that all of the cubic holes be occupied. In fact, the CsCl structure consists of a simple cubic array of Cl ^- ions with Cs⁺ ions filling all of the cubic holes.

Click on the image at right to view the CsCl structure. The links in the text above go to definitions.