Aluminum oxide (Al2O3) is a widely used industrial abrasive (corundum, emery), with its specific application depending on the hardness of the crystal
a) How is the hardness of an ionic material related to its lattice energy?
b) Knowing the relationships between lattice energy and: 1) charges and 2) atomic radii, would you have predicted that Al2O3 is hard? Explain your answer.