In an ideal Fluorite () crystal structure, the ions form a cubic close-packed (ccp) arrangement and — Solid State Chemistry Question
Question
In an ideal Fluorite ($CaF_2$) crystal structure, the $Ca^{2+}$ ions form a cubic close-packed (ccp) arrangement and the $F^-$ ions occupy the available voids. What is the coordination number of the $Ca^{2+}$ and $F^-$ ions respectively?
Answer: A
💡 Solution & Explanation
In the fluorite structure, $Ca^{2+}$ ions are in a ccp (fcc) lattice, and $F^-$ ions occupy all $8$ tetrahedral voids. Each $F^-$ is surrounded tetrahedrally by $4$ $Ca^{2+}$ ions, so its C.N. is 4. Each $Ca^{2+}$ ion is surrounded by $8$ $F^-$ ions in a cubic arrangement, making its C.N. 8. The coordination ratio is $8:4$.
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