Final answer:
Calcium oxide has a higher melting point than calcium iodide because of its stronger ionic bond and larger lattice energy due to the higher charges on the ions, Ca2+ and O2-, compared to Ca2+ and I- ions.
Step-by-step explanation:
The higher melting point of calcium oxide (CaO) compared to calcium iodide (CaI2) can be attributed to the type of bonding and lattice energy in the compounds. CaO is an ionic compound formed by strong electrostatic attraction between Ca2+ and O2- ions. This ionic bond is much stronger due to the higher charge of the ions involved, leading to a significant lattice energy, which is the energy required to separate one mole of a solid ionic compound into its gaseous ions.
In contrast, CaI2 consists of Ca2+ and I- ions. While it is still an ionic compound, the bond between the ions is weaker because iodide ions only carry a single negative charge. The lattice energy of CaI2 is lower, meaning less energy is required to disrupt the ionic lattice, leading to a lower melting point.
Based on lattice energy considerations and the ionic bonding nature of these compounds, it is expected that CaO, with its highly charged ions forming a very exothermic reaction upon lattice formation, would have a higher melting point than CaI2, which has a less exothermic lattice formation.
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