Question

A compound contains elements X and Y. Y atoms form CCP lattice and atoms of X occupy $\frac{1}{3}rd$ of tetrahedral voids. What is the molecular formula of the compound?

• A. XY
• B. $X_2{Y}_3$
• C. $X_3{Y}_2$
• D. $X{Y}_2$

Answer 1

Answer: (B)

$X_2{Y}_3$

Number of tetrahedral voids formed = $2\times NumberofatomsofelementY$

Number of atoms of element Y in the ccp unit cell = $4$

Number of tetrahedral voids formed = $2\times 4=8$

Number of tetrahedral voids occupied by atoms of $X$ = $\frac{1}{3}\times 8$

Ratio of the numbers of atoms of $X$ and $Y$ =$\frac{8}{3}:4=2:3$

Hence, the formula of the compound is $X_2{Y}_3$