Number of atoms per unit cell : Body Centered Cubic Unit Cell
In a body-centered cubic (bcc) unit cell, the atoms are present in the body-center besides the ones that are at its corners that wholly belongs to the unit cell in which it is present. Thus in a body-centered cubic (bcc) unit cell:
8 corners X 1/8 per corner atom = 8 * 1/8 = 1 atom
1 body center atom = 1 X 1 = 1 atom
Total number of atoms per unit cell = 2 atoms
Question: Niobium crystallises in body-centred cubic structure. If density is 8.55 g cm-3, calculate atomic radius of niobium using its atomic mass 93 u.
Answer: Density = 8.55 gcm-3
Consider length of the edge = a cm
Number of atoms per unit cell, Z = 2
M = 93 u
Using the formula
