Ionic Compounds

• Ionic compounds have a regular lattice structure
• The electrostatic attraction between the oppositely charged ions is ionic bonding
• Ionic compounds have a structure called a giant ionic lattice
• The ions form a closely packed regular lattice arrangement and there are very strong electrostatic forces of attraction between oppositely charged ions, in all directions in the lattice
• A single crystal of sodium chloride (table salt) is one giant ionic lattice. The Na+ and Cl- ions are held together in a regular lattice. The lattice can be represented in different ways
• This model shows the relative sizes of the ions, as well as the regular pattern of an ionic crystal, but it only lets you see the outer layer of the compound

  
• This is a ball ans stick model. It shows the regular pattern of an ionic crystal and shows how all the ions are arranged. It also suggests that the crystal extends beyond what's shown in the diagram. The model isn't to scale though, so the relative sizes of the ions may not be shown. Also in reality, there aren't gaps between the ions

  
• Ionic compounds all have similar properties
• They all have high melting points and high boiling points due to many strong bonds between the ions. It takes a lot of energy to overcome this attraction
• When they're solid, the ions are held in place, so the compounds can't conduct electricity
• When ionic compounds melt, the ions are free to move and they'll carry electric charge
• Some ionic compounds also dissolve in water. The ions separate and are all free to move in the solution, so they'll carry electric charge
• Empirical formula

  If it's a dot and cross diagram, count how many atoms there are of each element. Write this down to give you the empirical formula
• Empirical formula

  If you're given a 3D diagram of an ionic lattice, use it to work out what ions are in the ionic compound
• When working out the empirical formula from a diagram, after counting the elements, you'll have to balance the charges of the ions so that the overall charge is zero
• Example

  Work out the empirical formula of the ionic compound shown below.

  
  

  1) Look at the diagram to work out what ions are in the compound

  2) Work out what charges the ions will form

  3)Balance the charges so the charge of the empirical formula is 0

  
  

  > The compound contains potassium and oxide ions

  > Potassium in Group 1 so it forms 1+ ions, oxygen is in Group 6 so forms 2- ions

  > A potassium ion only has a 1+ charge, so you'll need 2 of them to balance out the 2- charge of an oxide ion

  
  

  = The empirical formula is K2O