In an ideal Fluorite () crystal structure, the ions form a cubic close-packed (ccp) arrangement and — Solid State Chemistry Question

💡 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 $8:4$.