Final answer:
The melting point of aluminum oxide is expected to be higher than that of calcium oxide due to the stronger electrostatic attraction between ions in Al2O3, which arises from the higher charge on the aluminum ions and their smaller size compared to the calcium ions in CaO.
Step-by-step explanation:
Would you expect the melting point of aluminum oxide to be higher or lower than that of calcium oxide? The melting point of aluminum oxide is expected to be higher than that of calcium oxide.
The melting point of a compound is greatly influenced by the strength of the bonds within its crystal lattice, which in turn is affected by the charge and size of the ions. Aluminum oxide (Al2O3), having a higher charge due to the presence of Al3+ ions compared to the Ca2+ ions in calcium oxide (CaO), will have a stronger electrostatic attraction between the ions. Furthermore, the aluminum ion is smaller than the calcium ion, leading to a denser crystal lattice and consequently a higher melting point.
This is also consistent with the fact that the lattice energy, which is higher when there is a greater charge and smaller ionic radii, will also be higher for Al2O3, as observed with CaO having a larger lattice energy than MgCl2 due to a higher charge on the oxide ion compared to the chloride ion.