Volume of KBr unit cell = a^3
                                     =
(0.65966 x 10^-9)^3
                                   Â
= 2.87 x 10^-22 cm^3
mass of 4 atoms in a unit cell = 4 x 119 g/mol/6.023 x 10^23
                                               =
7.90 x 10^-22 g
Bulk density = mass/volme
                    Â
= 7.90 x 10^-22/2.87 x 10^-22
                      =
2.75 g/cm^3
ionic radii for K ion and a touching Br atom =
a/2sq.rt.(2)
                                                                         Â
= 6.5966 x 10^-8 cm/2 x sq.rt.(2)
                                                                         Â
= 2.33 x 10^-8 cm
Result from ionic radii of K and Br = (1.52 + 182) pm
                                                     Â
= 3.34 x 10^-8 cm
So the radii calculated and the theoretical radii are close to
one another.
