Compute the theoretical density of caf2, which has the fluorite structure. ionic radii of ca2+ and f- are 0.100 nm and 0.133 nm respectively.

Calcium fluoride is a face centered cubic (FCC) lattice.The edge length (a) of the FCC lattice is equivalent to the 2×(radius of cation) + 4×(radius of anion)/1.414.For calcium fluoride, the cation is and anion is . On plugging the given values the edge length of the crystal lattice is {(2×1.00)+(1.33×4)/1.414} = 5.176 A°= 5.176X10⁻⁸cm (as 1nm=10A°).For FCC lattice number of atoms present per unit cell (Z)= 4.

Density of crystal, d= (Z X M)/(a³), where M is the molar mass of CaF₂= 74.03 g/mol. is Avogadro's number= 6.023 X 10²³ number of molecules. density, d= = 3.545 g/cm³.

So, theoretical density of CaF₂ is 3.545 g/cm³.

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