Question

An ionic compound $XY$ crystallizes in ideal $ZnS$ type structure. If the edge length of unit cell is $654\text{pm}$ then correct statement about this compound is-

• A. It has $BCC$ type unit cell
• B. $Z{n}^{2+}$ is present at body centre
• C. The structure has 4 : 4 coordination number
• D. Number of tetrahedral and octahedral voids are $4$ and $8$ respectively

Answer 1

The correct option is C The structure has 4 : 4 coordination number

In the Zinc Blende structure the ions are arranged in CCP(Cubic close Packing) manner. In the ccp arrangement there are 8 tetrahedral voids and 4 octahedral voids present.
The $S^{2-}$ ions are Present in FCC (Face centered Cubic) arrangement. i.e The $S^{2-}$ ions are present at the corner of the cube and at the center of each face.
The $Z{n}^{2+}$ ions are present at the alternative tetrahedral void.
Each $Z{n}^{2+}$ ion is surrounded tetrahedrally by four $S^{2-}$ ions and each $S^{2-}$ ion is surrounded tetrahedrally by four $Z{n}^{2+}$ ions. Thus the structure has 4:4 coordination.