Question

If Z is the number of atoms in the unit cell that represents the closest packing sequence ABCABC....., the number of tetrahedral voids in the unit cell is equal to

• A. Z
• B. Z/2
• C. 2Z
• D. Z/4

Answer 1

The correct option is C 2Z

The close packing sequence ABCABCABC... represent the cubic close packing structure. Here, Z is the number of atoms in the unit cell.
In ccp/fcc, there are two tetrahedral voids on the every body diagonal of the cube/unit cell.
Fcc has total 4 body diagonals. Thus, totally 8 tetrahedral voids present inside the unit cell.
Also, number of atoms in fcc/ccp arrangement is 4
Hence,
$\text{No. of atoms per unit cell}=Z$
$\text{No. of tetrahedral voids}=2Z$