Question

What is the void space of a FCC unit cell?

Answer 1

Hint: This question gives the knowledge about the fcc crystal lattice. Fcc crystal lattice is called as face-centered cubic crystal lattice. It contains six atoms at each face of the cube and eight atoms at the corners of the cube. Diamond experiences cubic crystal structure.

Complete answer:
Fcc crystal lattice contains six atoms at each face of the cube and eight atoms at the corners of the cube. The effective number of atoms in a fcc crystal unit cell is always $4$. The coordination number of FCC lattice is $12$. The elements which possess face centered unit cells are copper, aluminum, silver and so forth. Face centered crystal lattice is a closed packed structure.
Void is defined as the empty space between the molecules present in the crystal lattice. The void space of the face centered cubic unit cell is equal to the difference between the total space occupied by the face centered crystal lattice and the packing efficiency of the unit cell.
The packing efficiency of the face centered unit cell is $74\% $ and the total space occupied by the face centered unit cell is $100\% $. So, the difference between the total space occupied by the face centered crystal lattice and the packing efficiency of the unit cell is $26\% $.

Therefore, the void space of FCC unit cells is $26\% $.

Note:
Always remember that the effective number of atoms in a face centered cubic crystal unit cell is always $4$. FCC crystal lattice contains six atoms at each face of the cube and eight atoms at the corners of the cube.It is also called cubic closest packing.