Question

In the calcium fluoride structure the coordination number of the cation and anions are respectively

• A. 6, 6
• B. 8, 4
• C. 4, 4
• D. 4, 8

Answer 1

Answer: (B)

In calcium fluoride structure, the $C{a}^{2+}$ ions are arranged in ccp (cubic closed packed) arrangement, $ie,C{a}^{2+}$ ions are present at all corners and the centre of each face of the cube. The fluoride ions occupy all the tetrahedral sites. This is $8:4$ arrangement ie, each $C{a}^{2+}$ ion is surrounded by $8F^{-}$ions and each $F^{-}$ion by four $C{a}^{2+}$ ions.