structure of fluorite

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 Fluorite structure : 


In CaF², the radius radio is 0.732 which gives rise to a body - centred cubic (bcc) structure. In this case each Ca²+ ion is surrounded by eight F- ions, so the co-ordination number of Ca²+ is 8. Since in an ionic compound containing different numbers of cation and anions, the cation and anion have different co-ordination numbers, it follows that the co ordination number of F- ion is four (since the number of F- ions is double the number of Ca²+ions). Thus, CaF² has 8 : 4 arrangements. In fluorite, Ca²+ ions are too small to touch each other hence, the structure is not strictly close packed structure. 

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