Question

In an oxide of aluminium, oxide ions are arranged in ccp arranged and the aluminium ions occupy two third of the octahedral voids. what is the formula of the compound?

Answer 1

Effective number of oxide ions $\Rightarrow Z_{O^{2-}}=4$

Effective number of Aluminium ions $=\frac{2}{3}\times$Octahedral voids $=\frac{2}{3}\times 4=\frac{8}{3}$

Formula

$\Rightarrow A{l}_{\frac{8}{3}}{O}_4\Rightarrow A{l}_2{O}_3$