Question

The unit cell cube length for $LiCl$ is $5.14\stackrel{o}{A}$. Assuming anion-cation contact, calculate the ionic radius for chloride ion.

Answer 1

In $LiCl$ structure, anions have face centered cubic arrangements. In such a unit cell face diagonal is four times the radius of anions.

Face diagonal $=\sqrt{2}.a=\sqrt{2}\times 5.14A^0$

Face diagonal $=4r$

$\therefore$ $4r=\sqrt{2}\times 5.14A^0$

$\Rightarrow r=1.82A^0$