In corundum oxide, ions are arranged in HCP array and the aluminum ions occupy two-thirds of octahedral voids. What is the formula of corundum?

Asked by Topperlearning User | 4th Jun, 2014, 01:23: PM

Expert Answer:

In a close packing (hcp) or (ccp) there is one octahedral void corresponding to each atom constituting the close packing.

In corrundum only two thirds of octahedral voids are occupied. It means that corresponding to each oxide ion there 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.

Answered by  | 4th Jun, 2014, 03:23: PM