How many atoms constitute one unit cell of a face-centered cubic crystal?

Face centred cubic unit cell has points at the corners as well as at the centres of each of the six face.

The contribution of each atom at the face per unit cell is as each face atom exists in 2 adjacent cells, and at each corner, it is as each corner atom exists in 8 adjacent cells.

So, number of atoms present at corners per unit cell = (8 corner atoms x atom per unit cell) = 1 atom.

Number of atoms present at faces per unit cell = (6 atoms at faces x atom per unit cell) = 3 atoms.

∴ Total no. of atoms per unit cell = 3+1= 4 atoms.

Face centred cubic lattice.