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) `4Br^(–), 4k^(+)` (b) 6.56Å (c) 2.80 gm/cc (d) 0.414