Ionic compounds are a type or kind of chemical compound. Ionic compounds are compounds where the atoms are bonded together through electric charges caused by atoms giving or taking electrons from other atoms. Remember that atoms are unstable, and that to become stable they need to either gain or lose electrons. When they do this, they form ions. Like magnets, oppositely charged ions attract each other and stick together. This kind of bonding is very strong because the atoms are like very strong magnets. They have given electrons to each other and now can't leave. Because of this bond, ionic compounds have certain properties:
  • They are always made of a metal and a non-metal or an element and a polyatomic ion.
  • Ionic compounds have a neutral (that means zero) electric charge.
  • Many ionic compounds can dissolve in water, but not all of them.
  • Ionic compounds have very high melting and boiling points.
  • Ionic compounds do not form molecules. Instead they form crystals made up of 'formula units', pieces of them which have the same chemical formula as the compound. For example, salt is sodium chloride: NaCl. A piece of salt is not a collection of NaCl molecules all in one place. Instead it is a collection of sodium cations and chlorine anions arranged in a certain way in a 1-to-1 ratio.
  • Ionic compounds, in large crystal forms, tend to be hard but brittle. This means they break instead of stretch, but they tend to be hard to damage (either by scratching or by smashing).
  • Ionic compounds are stronger when you stack things on them than when you hang things from them. This makes them very good building materials. Concrete, cement, and all kinds of stone and ceramics are ionic compounds.
  • Ionic compounds are poor conductors of electricity in solid form, but they are very good conductors of electricity when dissolved in a liquid, such as water.