Since very strong electrostatic forces of attraction are present between the ions within a crystal lattice, a significant amount of energy is needed to break these forces. This is the reason why the melting points of ionic compounds are generally very high. During the process of melting these attractive forces break down and let the ions move freely.
The melting points of ionic compounds (salts) depend upon the charges present on the ions and their sizes. Higher charges and smaller ion sizes lead to stronger attractions and hence the higher melting points.
strong lattice
closer attraction
📘 notes from text: “very strong electrostatic forces … within crystal lattice … significant energy to break. During melting forces break → ions free. Melting points depend on charges & ion sizes. Higher charges & smaller sizes → stronger attraction → higher melting point.”