Question

How many number of atoms are present in each unit cell in ccp structure?

Answer 1

ccp structure:

• Cubic closed packing(ccp) contains three different layers, in which, the third layer is not aligned with the first two layers, so its arrangement pattern is ABCABC.
• It is also known as face-centred packing also.
• The structure of ccp or fcp is shown as,

• A constituent particle present at the centre is shared by two neighbouring cells, thus its contribution is only $\frac{1}{2}$.
• A constituent particle present at the corner is shared by eight neighbouring cells, thus its contribution is only $\frac{1}{8}$.
• The total number of atoms present on the face of the unit cell is, $6\times \frac{1}{2}=3$.
• The total number of atoms present on the corner of the unit cell are, $8\times \frac{1}{8}=1$.
• The total number of atoms present in the unit cell, $3+1=4$.

Hence, a total of four atoms are present in each unit cell of the ccp structure.