Calculate the ratio of the alkali metal bromides on the basis of the data given below and predict th

Calculate the ratio of the alkali metal bromides on the basis of the data given below and predict the form of the crystal structure in each case. Ionic radii (in pm) are given below Li+ = 74,         Na+ = 102,         K+ = 138 Rb+ = 148,      Cs+ = 170,         Br- = 195

Answer -

The ratio of cation to that of anion i.e. r+/r– gives the clue for crystal structure Li+ / Br–   74 / 195 = 0.379  Tetrahedral

Na+ / Br–  102 / 195 = 0.523  Octahedral

K+ / Br–  138 / 195 = 0.708  Octahedral

Rb+ / Br–  148 / 195 = 0.759 Body centered

Cs+ / Br– 170 / 195 = 0.872 Body centered