* Strong electrostatic forces: Ionic compounds are held together by strong electrostatic forces of attraction between oppositely charged ions. These forces are very strong and require a significant amount of energy to overcome.

* Crystal lattice structure: The ions in ionic compounds form a highly ordered, three-dimensional crystal lattice. This arrangement maximizes the electrostatic attractions between the ions, making the structure very stable.

* High energy required for melting: To melt an ionic substance, you need to provide enough energy to break the strong electrostatic bonds holding the ions together. This requires a lot of heat, resulting in high melting points.

Examples:

* Sodium chloride (NaCl) has a melting point of 801°C.

* Magnesium oxide (MgO) has a melting point of 2852°C.

Exceptions:

While most ionic compounds have high melting points, there are some exceptions:

* Compounds with large ions: When ions are very large, the electrostatic forces holding them together are weaker. This can result in lower melting points.

* Compounds with low charge density: If the charges on the ions are relatively small, the electrostatic forces will be weaker, leading to lower melting points.

Overall, it's safe to say that ionic substances are generally known for their high melting points due to the strong forces holding their crystal lattices together.