Simple ionic solids usually have more complicated structures than metals. The structure of a metal is usually determined by the packing of spheres of the same size. The structure of a simple ionic compound is usually determined by the packing of spheres of differing sizes.

For example:
Cesium metal:
    cesium atomic radius: 267 pm

Cesium iodide:
    cesium ionic radius: 169 pm
    iodide ionic radius: 219 pm

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