Question

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

Answer 1

Hint: Crystal structure is a description of the orderly organisation of atoms, ions, or molecules in a crystalline substance used in crystallography.
The most basic and least volume-consuming repeating structure of any material is the unit cell. Its purpose is to visually simplify the crystalline patterns that solids form. The network is called a lattice when the unit cell repeats itself.

Complete answer:
The spheres of the third layer are not aligned with those of the first or second layers in cubic tight packing. So, if the first layer is represented by a ‘A,' the second layer by a ‘B,' and the third layer by a ‘C,' the precise pattern of layers may be expressed as ABCABC. A cubic close-packed (ccp) or face-centred cubic (fcc) structure is the name given to this crystal structure.
Atoms are arranged at the four corners and the centre of each cube face in a face-centred cubic unit cell. Only half of each atom belongs to each individual cell, while the atom at the centre of the face is shared by two neighbouring unit cells.
Cubic close packing (CCP) is another term for face-centered cubic packing (FCC). They both have the tightest atom packing conceivable. The layers of planar sheets of atoms, on the other hand, are structured in a somewhat different way. The number of atoms per unit cell in a ccp or fcc structure is computed as follows.
We have the following in a face-centred cubic unit cell (fcc) or cubic close packing (ccp):
8 corners with ${\displaystyle \frac{1}{8}}$ atom each corner = 8 x ${\displaystyle \frac{1}{8}}$ = 1 atom
6 face-centered atoms divided by ${\displaystyle \frac{1}{2}}$ atom per unit cell equals 3 atoms
As a result, a unit cell's total number of atoms is equal to four.

Note:
The hexagonal closest packed (hcp) has 6 atoms per unit cell and has a coordination number of 12. The face-centered cubic (fcc) has a coordination number of 12 and a unit cell size of 4 atoms. The body-centered cubic (bcc) has an eight-coordinate coordination number and two atoms per unit cell.