Properties of Ionic Compounds
Simple Explanation
Ionic compounds share a distinctive set of properties: high melting and boiling points, they form hard but brittle crystals, and they conduct electricity when dissolved in water or melted — but not as a solid.
Why Do We Need It?
Recognizing these properties lets you identify an unknown substance as ionic just from how it behaves, without needing to already know its formula — and explains why we use salt solutions (not solid salt) in electrical and biological systems that rely on ion conduction.
Why Does This Work?
All of these properties trace back to the same cause: a rigid 3D lattice held together by strong electrostatic attractions in every direction. Breaking the lattice apart (melting) takes a lot of energy, hence high melting points. A blow that shifts one layer of ions relative to another suddenly lines up same-charge ions, which repel and shatter the crystal — hence brittleness. And solid ions are locked in place and cannot move to carry current, but once melted or dissolved they become free to move, which is what conducts electricity.
Real-Life Example
Why you add salt to melting ice, and why saltwater conducts electricity
Road salt (NaCl) is spread on icy roads, and seawater conducts electricity while pure water barely does.
Dissolved in water, NaCl separates into freely-moving Na⁺ and Cl⁻ ions — this both lowers the freezing point of the water (helping melt ice) and lets electric current flow through the solution, since the mobile ions carry charge.
Practice
Why does solid sodium chloride NOT conduct electricity, while molten (liquid) sodium chloride does?
MediumCommon mistake
Assuming ionic compounds simply 'don't conduct electricity' — the accurate statement is that they don't conduct as solids, but do conduct once melted or dissolved, because that's when the ions become mobile.
Quick Review
- Ionic compounds have high melting/boiling points from strong lattice attractions.
- They are hard but brittle — a shift in the lattice brings like charges together and shatters it.
- They conduct electricity only when molten or dissolved, not as a solid.