Question:   How does the melting point of a substance depend on the type of bonding in the substance?

Answer:

Ionic compounds have higher melting (and boiling) points than covalent compounds.  You can think of it like this:  In an ionic compound, all of the ions are like little magnets.  As a result, all of the magnets stick to each other tightly, making them hard to pull apart (you have to actually break ionic bonds to melt the compound).

On the other hand, in a covalent compound, what you find is molecules containing tightly-bonded atoms, but the molecules themselves are held together only by intermolecular forces.  Since intermolecular forces are far weaker than regular bonds, it's easy to pull covalent molecules apart from one another.