Why do ionic compounds have high melting and boiling points?

• A. Ionic bonds are very strong, requiring a large amount of energy to break.
• B. They have covalent networks that are easily broken.
• C. They are always non-polar.
• D. They consist of large molecules with weak forces.

Answer: (A)

High melting and boiling points come from the strong forces holding the lattice together. In ionic compounds, oppositely charged ions are arranged in a crystal and attract each other very strongly. To melt or boil the substance, you have to break many of these electrostatic attractions throughout the whole lattice, which takes a lot of energy. This is why ionic compounds tend to have high melting and boiling points. The strength of these forces—lattice energy—depends on the charges of the ions and how closely they are packed, so compounds with highly charged, small ions have especially high points.

The other statements don’t fit: they refer to covalent networks or weak forces, or imply non-polarity, which isn’t the defining feature of ionic solids.