Ionic compounds have high melting points due to the strong electrostatic forces of attraction between positively and negatively charged ions in the crystal lattice structure. Ionic compounds are composed of ions, which are formed when electrons are transferred from one atom to another. One atom loses electrons to form a positively charged ion (cation), and another atom gains those electrons to form a negatively charged ion (anion).

The positive and negative ions are held together in a three-dimensional array or lattice structure by strong electrostatic forces of attraction, often referred to as ionic bonds. These forces are quite strong and require a significant amount of energy to overcome, which is why ionic compounds generally have high melting and boiling points.

To melt or boil an ionic compound, you need to provide enough energy to break the ionic bonds and separate the ions. The higher the melting point, the more energy is required to overcome these strong forces of attraction.

In contrast, covalent compounds, where atoms share electrons rather than transfer them, generally have lower melting points because the forces holding the molecules together (intermolecular forces) are weaker than the ionic bonds in ionic compounds.