Question

An ionic solid XY has BCC structure with edge length equal to 4.4 A. the minimum distance between two oppositely charged ions is?

Answer 1

An ionic solid XY has BCC (body centered cubic lattice structure).

then, $r_{X^+}+r_{Y^-}=\frac{\sqrt{3}a}{2}$

where $r_{X^+}$ is radius of cation , $r_{Y^-}$ is radius of anion and a is edge length of lattice.

given, edge length of lattice = 4.4A°

so, $r_{X^+}+r_{Y^-}=\frac{\sqrt{3}4.4}{2}=2.2\sqrt{3}$

or, $r_{X^+}+r_{Y^-}$ = 3.81A°

hence, minimum distance between two oppositely charged ions is 3.81A°