I have no idea, but I'm sure our chemistry guys will weigh in.
In the meantime, I find it hard to believe that you would be given such a question without having studied something like it already. How can you possibly have "no idea" where to start? Check your text or google face-centered lattices for ideas.
Calcium Fluoride, CaF2, adopts the fluorite lattice, which is described as a face-centered cubic array of Ca2+ ions with F-1 ions with Ca2+ ions in half of the cubic holes. The Radii of Ca2+ and F-1 are 126 and 117 pm, respectively. Calculate the density of CaF2 from these data. Please give me somewhere to start. I am completely lost on this question.
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There was two slides over this, but they both involved one element.
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