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
There is one octahedral hole for each atom in
hexagonal closed packed arrangement. If the number of oxides ions per unit cell is x, then
Number of Fe3+ ions = 2/3 X octahedral holes
2/3 x=2x/3
.•. Ratio of Fe3+: O2- = 2x/3 : x = 2:3
Thus, formula of compound = Fe203