How do ionic and molecular compounds compare in terms of melting points?
Ionic compounds are held together by electric attractions between positive and negative ions. These are ionic bonds, and these bonds keep the ions together in a regular 3-d pattern (a crystal lattice)
To melt an ionic substance, you have to disrupt these bonds. This requires a lot of energy.
Molecules are held together by covalent bonds, which are strong. But you do not need to break these covalent bonds when melting a molecular substance. In molecular solids, each molecule is neutral and it is attracted to its neighboring neutral molecule by an intermolecular force (3 types: dispersion forces, dipole-dipole force, and hydrogen bonding).
To melt a molecular substance, you need to break these weak intermolecular forces between neutral molecules, which is why ionic compounds generally have much higher melting points than molecular compounds.