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

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

CMC MedicalCMC Medical 2011

Solution:

In $ Ca{{F}_{2}}, $ the $ C{{a}^{2+}} $ ions are arranged in ccp arrangement, i.e., $ C{{a}^{2+}} $ ions are present at all the comers and at the centre of each face of the cube. The fluoride ions occupy all the tetrahedral sites. In the $ Ca{{F}_{2}} $ structure, each $ {{F}^{-}} $ ion is surrounded by four $ C{{a}^{2+}} $ ions while each $ C{{a}^{2+}} $ ion is surrounded by eight $ {{F}^{-}} $ ions. Hence, the coordination numbers of $ C{{a}^{2+}} $ and $ {{F}^{-}} $ ions are 8 : 4.