Question

Ferric oxide crystallises in a hexagonal close-packed array of oxide ions with two out of every three octahedral holes occupied by ferric ions. Derive the formula of the ferric oxide.

Answer 1

Ferric oxide crystallizes in hcp and the oxide ions are present in the lattice sites, so the number of atoms =6;

ferric ions occupy the octahedral voids, and the occupancy = 2/3;

no of octahedral voids = 6;

octahedral voids occupied = 2*6/3 = 4;

therefore the formula of ferric oxide is;

Fe 4 O6 or Fe2O3.Gold (atomic radius = 0.144 nm) crystallises in a face-centred unit cell.

Answer 2

Ferric oxide crystallises in a hexagonal close-packed array of oxide ions with two out of every three octahedral holes occupied by ferric ions. Derive the formula of the ferric oxide.