Which statement best describes ionic solids in the solid state?

• A. Very low melting points.
• B. Excellent electrical conductors in the solid state.
• C. Very high melting points.
• D. Flexible and easily deform.

Answer: (C)

Ionic solids have a rigid crystal lattice built from positively and negatively charged ions held together by strong Coulombic forces. Because these ionic bonds are so strong, a lot of energy is needed to break the lattice and melt the solid, giving ionic solids very high melting points. In the solid state, the ions are fixed in place, so there’s little to no mobility; this means they do not conduct electricity as solids (they only conduct when melted or dissolved, where ions can move). The idea that they are very low melting points or flexible and easily deformed contradicts the reality of the stiff, brittle crystal structure and strong bonding. Thus, the statement that best describes ionic solids in the solid state is that they have very high melting points.