why in CaF2, F- ions occupy voids even though they are anions although anions are supposed to form close packed structures and cations are supposed to occupy voids?

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Solution

In an ionic solid the larger ion forms the closed packed structure and the smaller ion occupies the voids. The cations are formed by the loss of valence electrons (outermost shell) while anions gain electrons and generally, the anions are larger in size to the cations. In CaF₂, Ca²⁺ is larger in size to F^-and hence Ca²⁺ forms the closed packed structure and anions occupy the voids.

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