Question

In a body centred and face centred arrangement of atoms of an element, what will be the number of atoms present in respective unit cells? Justify your answer with calculation.

Answer 1

Body centred cubic : Number of atoms at the corners per unit cell $=\frac{1}{8}\times 8=1$
Number of atoms present at the centre of the cube $=1$
$\therefore$ Total number of atoms in bcc arrangement $=1+1=2$
Face centred cubic : Number of atoms present at the corners per unit cell $=\frac{1}{8}\times 8=1$
Number of atoms present at the faces per unit cell $=\frac{1}{2}\times 6=3$
$\therefore$ Total number of atoms in fcc arrangement $=1+3=4$