Question

In cubic ZnS, the radii of the Zn and S atoms are 0.83 Å and 1.74 Å respectively. What is the edge length of the unit cell of ZnS ?

• A. 2.57 Å
• B. 3.64Å
• C. 2.97Å
• D. 5.935Å

Answer 1

Answer: (D)

5.935Å

Answer 2

Let edge length of the unit cell = a

$\sqrt{3}$ × $\frac{a}{2}$× $\frac{1}{2}$ = $r_{Zn^{2 +}}$ + $r_{S^{2 -}}$

or $\sqrt { 3 }$ $\frac{a}{4}$= 0.83 + 1.74 = 2.57

or a = 2.57 × $\frac{4}{\sqrt{3}}$ = 5.935 A⁰