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 aluminum?

Answer 1

(i) For cubic close-packed structure

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

= 4.4 x 10⁷ pm³

= 4.4 x 10⁷ x 10⁻³⁰ cm³

= 4.4 x 10⁻²³ cm³ 

Therefore, number of unit cells in 1.00 cm³

= 1.00 cm³/4.4 x 10 ^-23 cm³

= 2.27 x 10²²