Ionic compounds have high melting points because their ions are held together by very strong electrostatic attractions in a rigid 3D lattice, and a large amount of energy is needed to overcome these forces and allow the ions to move freely as a liquid.

Core idea: strong ionic bonds

  • Ionic compounds are made of positively charged cations and negatively charged anions arranged in a regular crystal lattice.
  • Opposite charges attract strongly, creating electrostatic forces (ionic bonds) that are much stronger than typical intermolecular forces in many molecular substances.

Why this gives high melting points

  • To melt an ionic solid, the ions must be separated from their fixed positions in the lattice, which means overcoming many strong attractions all at once.
  • Supplying this energy requires high temperatures, so the temperature at which the solid becomes a liquid—that is, its melting point—is very high.

Quick classroom-style answer

Ionic compounds have high melting points because their oppositely charged ions are strongly attracted to each other in a closely packed lattice, so a large amount of heat energy is needed to break these strong ionic bonds.

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