Structure of Al2O3 Watch
Now I understand everything except the last statement.
Can anyone describe it for me ?
I think the use of the word "lattice" there was perhaps a poor choice. What they must mean is "strong covalent bonds throughout the giant structure". By giant structure this means something similar to that formed by diamond or SiO2 where the atoms are all held together by covalent bonds rather than intermolecular forces between discrete molecules. Al2O3 has some of this character in its bonding as well some character of an ionic lattice.
Forgive me if I'm wrong, but I've always thought that it would be ionic - 2 Al3+ ions and 3 O2- ions bonded together ionically - two aluminium atom transferring 6 electrons to three oxygen atoms.