Properties of ionic compounds
ionic compoundAn ionic compound occurs when a negative ion (an atom that has gained an electron) joins with a positive ion (an atom that has lost an electron). have regular structures, called giant ionic latticeThe regular arrangement of ions in an ionic substance.. In a giant ionic lattice, there are strong electrostatic forces of attraction acting in all directions between the oppositely charged ions. The structure and bonding of ionic compounds explain their propertiesThe characteristics of something. In chemistry, chemical properties include the reactions a substance can take part in. Physical properties include colour and boiling point..
Learn more on properties of ionic compounds in this podcast.
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High melting points and boiling points
Energy must be transferred to a substance to make it melt or boil. This energy overcomes the strong electrostatic forces of attraction which act in all directions between the oppositely charged ions:
- some forces are overcome during melting
- all remaining forces are overcome during boiling
The more energy needed, the higher the melting pointThe temperature at which a solid changes into a liquid as it is heated. or boiling pointThe temperature at which a substance rapidly changes from a liquid to a gas.. Since the electrostatic forces of attraction between oppositely charged ions are strong, their melting and boiling points are high.
| Compound | Melting point | Boiling point |
| NaCl | 801掳颁 | 1413掳颁 |
| MgO | 2852掳颁 | 3600掳颁 |
| Compound | NaCl |
|---|---|
| Melting point | 801掳颁 |
| Boiling point | 1413掳颁 |
| Compound | MgO |
|---|---|
| Melting point | 2852掳颁 |
| Boiling point | 3600掳颁 |
You can see from the data in the table that sodium chloride is a solid below 801掳颁, a liquid between 801掳颁 and 1413掳颁, and a gas at temperatures higher than 1413掳颁.
Conducting electricity
A substance can conductTo allow electricity, heat or other energy forms to pass through. electricity if:
- it contains charged particlesParticles, usually ions or electrons, that carry electrical charges., such as ions, and
- these particles are free to move from place to place
An ionic compound can conduct electricity when:
- it has moltenA term used to describe a liquid substance (eg rock, glass or metal) formed by heating a solid. to form a liquid, or
- it has dissolved in water to form an aqueousDissolved in water to form a solution. Shown as (aq) in chemical equations. solution
Both these processes allow ions to move from place to place. Ionic compounds cannot conduct electricity in the solid state because their ions are held in fixed positions and cannot move.