Question

Sapphire is aluminium oxide. It crystallises with aluminium ions in two thirds of octahedral holes in a closest packed array of oxide ions.

Answer 1

Answer:

The molecular formula of sapphire is $Al_{\frac{2}{3}}O_1=Al_2O_3$

Explanation:

Number of oxide ions in cubic close packing = n = 1

Number of octahedral voids = n = 1

n = number of spheres in the packing

Aluminium ions in two thirds of octahedral holes =$\frac{2}{3}n=\frac{2}{3}\times 1=\frac{2}{3}$

The molecular formula of sapphire is $Al_{\frac{2}{3}}O_1=Al_2O_3$