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Dot and cross diagrams help us to model when ions are formed from atoms.

Here’s an example using sodium and chlorine. They form ions which bond to form sodium chloride.

1. Draw the electronic configuration of each atom – one element with dots and the other with crosses.

2. Work out how many electrons need to be transferred.

3. Draw the electronic configuration of the resulting ions.

4. Write the charge of each ion.

Here are some other examples of dot and cross diagrams for the formation of ions in some ionic compounds – magnesium oxide and calcium chloride.