Question

for k+ and Br- find the radius ratio of K+ ion and B r- ion and on this basis predict the shape of crystal geometry of KBr.Draw a diagram indicating the arrangement of K+ and Br- ions in crystal of KBr.

Answer 1

K+/Br-

 

ratio is 152 pm/182pm = 0.835. Thus, it must be cubic structure with CN = 8

 

Answer 2

Ionic radius ratio is defined as the ratio of the radius of cation to the radius of the anion.
--->Ionic Radius ratio helps us in determining the coordination number.
---->It gives us clues regarding the nature of crystal structure of Ionic substance.

In K⁺/Br⁻  radius of K⁺/radius of Br⁻  =133pm/196pm =0.678
Structure :
As the KBr ionic radius is in the range of 0.414 to 0.732
Therefore The lattice structure of KBr is same as NaCl type Crystal structure and octahedral geometry.
--->Thus KBr has rock salt structure---
--->Therefore coordination number of each ion is 6.
--->The Lattice structure consist  of  a face centered cube of Br- ions with a K + ion occupying each of the octahedral holes.