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 CCP structure, edge length, a = 2√2r = 2√2 x 125 pm = 354 pm 

(ii) volume of unit cell = a³ = (354 × 10^-8m)³ 

∴ Number of unit cells in 1.00 cm³ 

= \(\frac{1}{(354 \times 10^{-8})^3} \) = 2.26 x 10²²