Question

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?

Answer 1

(i) For cubic close-packed structure:

= 353.55 pm

= 354 pm (approximately)

(ii) Volume of one unit cell = (354 pm)³

= 4.4 × 10⁷ pm³

= 4.4 × 10⁷ × 10⁻³⁰ cm³

= 4.4 × 10⁻²³ cm³

Therefore, number of unit cells in 1.00 cm³ =

= 2.27 × 10²²