Question

The unit cell cube length for $LiCl$ (just like $NaCl$ structure) is $5.14\mathring{A}$. Assuming anion-anion contact, the ionic radius for chloride ion is:

• A. $1.815\mathring{A}$
• B. $2.8\mathring{A}$
• C. $3.8\mathring{A}$
• D. $4.815\mathring{A}$

Answer 1

The correct option is A $1.815\mathring{A}$

In NaCl structure, anions have face centered cubic arrangement.

In such a unit cell face diagonal is four times the radius of anions.

Face diagonal $=\sqrt{2}a=\sqrt{2}\times 5.14\mathring{A}$

Face diagonal $=4r$

$4r=\sqrt{2}\times 5.14$

$r=\frac{\sqrt{2}\times 5.14}{4}=1.817\mathring{A}$