Aluminium crystallises in a cubic close-packed structure. Its metallic radius is 125 pm.
(i) What is the length of the side of the unit cell?
(ii) How many unit cells are there in 1.00 cm3 of aluminium?
Given, radius of atom = 125 pm
i) for ccp structure, we know that
where, r = radius and a = length of side
125 pm
a = 125 × 
pm
a = 125 × 2 × 1.414 pm
a = 353.5 pm
ii) volume of one unit cell = a3
= (353.5 × 1- -3cm)3
= 44192902.36 × 10-30
= 442 × 10 -25 cm 3
Thus, number of unit cell of aluminium in 1 cm3
=
= 2.27 × 10 22 unit cell.
25