Question

Find the radius ratio of caf2

Answer 1

10.4 The CaF2 (fluorite) structure

A unit cell representation of fluorite structure is shown in the figure.


The calcium ions are marked as green spheres, and fluoride ions are marked as light blu sphere. Its structure can be described as:

The calcium ions form the ccp arrangement, i.e., these ions occupy all the corner positions and the center of each face of the cube.Fluoride ions are so located that there are four calcium ions around it. It may be said that the fluoride ions occupy tetrahedral sites and the coordination number of fluoride ion is 4.As there are two tetrahedral sites available for every calcium ion, the fluoride ions occupy all the tetrahedral sites. The stochiometry of the compound is 1:2.Each fluoride ion is surrounded by four calcium ions whereas each calcium ions is surrounded by eight fluoride ions which are disposed towards the cornersof a cube. The coordination of the compound is 8:4

Other examples of compounds which show this type of structure are SrF2, BaF2, SrCl2, CdF2, HgF2, and PbF2.