KBr crystallizes in NaCl type of unit cell. `K^(+)` radius `= 1.33Å, Br^(-) " radius " = 1.95Å`
(a) How many `K^(+)` ions and how many `Br^(-)` ions are in each unit cell ?
(b) Assuming the additivity of ionic radii, what is a ?
(c) Calculate the density of a perfect KBr crystal
(d) What minimum value of `r_(+)//r_(-)` is needed to prevent anion-anion contact in this structure

Answer

(a) `K^(+)` ion = 4 & `Br^(-)` ion = 4 (b) `6.56 Å` (c) `2.80 g//cm^(3)` (d) 0.414