Question

Explain how much portion of an atom located at
A) Corner

B) Body-centre

of a cubic unit cell is part of its neighbouring unit cell.

Answer 1

A) Portion of atom at corner in unit cell

An atom located at the corner of a cubic unit cell is shared by eight adjacent unit cells. Thus, a one-eighth portion of the atom is shared by one unit cell.

B) Portion of atom at body-centre in unit cell

An atom located at the body centre of a cubic unit cell is not shared by its neighbouring unit cell. Hence, the atom belongs only to the unit cell in which it is present, i.e., its contribution to the unit cell is $1$.