Question

In crundum oxide ions are arranged in hcp array and al ions occupy 2/3rd of octahedral voids.what is the formula of corundum

Answer 1

In ccp or hcp packing there is one octahedral void corresponding to each atom constituting the close packing. In corundum only 2/3rd of the octahedral voids are occupied. It means corresponding to each oxide are 2/3 aluminium ions. The whole number ratio of oxide and aluminium ion in corundum is therefore 3:2 Hence formula of corundum is Al2O3

Answer 2

Answer:The formula of corundum :$Al_2O_3$

The metal oxide formula is .

Explanation:

Number of oxide ions in HCP = 4

Number of octahedral voids = n = 4

n = Number of spheres in the packing

Number of Al ions occupying the octahedral voids = $4\times \frac{2}{3}=\frac{8}{3}$

Formula of metal oxide  =$Al_{\frac{8}{3}}O_4=Al_2O_3$

The formula of corundum :$Al_2O_3$