Ionic compounds are giant structures, this means that they consist of large numbers of ions. An ionic compound is made of metallic and non-metallic ions, metal ions have a positive charge and non-metal ions have a negative charge. The oppositely charged ions attract each other (can also be called an electrostatic attraction) and form a crystalline lattice like the one shown to the right. These attractions go in all dirsctions.
In a crystalline lattice the particles are arranged to maximise the attractive forces between the ions, or in simpler terms the non-metal and metal ions alternate. This is shown in the diagram to the right, you're expected to know the 2D structure of sodium chloride.If you're asked to draw this in an exam - you must draw the 2D form containing at least 9 ions in a 3 x 3 grid.
2D representation of a crystal lattice.
3D representation of a crystal lattice.
Ionic Compounds have the following physical properties:
Explaining the properties of ionic compounds features in every higher tier exam and are worth a minimum of 2 marks, normally 4 for hardness and melting/boiling point, so learn these model answers off by heart. Simplified questions worth two marks normally appear in the foundation tier.
Ionic substances are hard because there are strong electrostatic attractions between oppositely charged ions in a giant structure, therefore a lot of force is needed to overcome this attraction and break the ions apart.
Ionic substances have high melting and boiling points because there are strong electrostatic attractions between oppositely charged ions in a giant structure, therefore a lot of energy is needed to overcome this attraction and break the ions apart.
When molten or dissolved the ions are able to move, so charge can flow freely.
N.B. The charge in this case is the physical movement of the ions. Be careful when looking at older markschemes - AQA have changed what they will allow as an acceptable answer to this question.