Explain the calculation of the number of atoms in a primitive cubic unit cell.

(N/A) - $A$ primitive cubic unit cell has atoms only at its corners. Each atom at the corner is shared between $8$ adjacent unit cells as shown in the figure. Four unit cells are in the same layer and four unit cells are in the layer above or below.
- Only $\frac{1}{8}$ of an atom,molecule,or ion is included in a particular unit cell.
- In the following figure,primitive cubic unit cells are shown: $(a)$ open structure,$(b)$ space-filling structure,$(c)$ actual portion of atoms included in each unit cell. In figure $(a)$,each small sphere represents the center of the particle at its position. It does not represent the actual size. Such structures are called open structures. Overall,there are $8$ atoms at the corners of each cubic unit cell.
- $\therefore$ Total number of atoms in one unit cell $= 8 \times \frac{1}{8} = 1$.