Elements “aim” to have a full outer shell. They can do this in a number of ways. One method is for atoms to gain or lose electrons.
Because atoms cannot change the number of protons that are in the nucleus this means they would have a different number of protons to electrons. If protons and electrons are not balanced then there must be a charge.
They can gain a full outer shell by losing electrons and becoming positive or gaining electrons and becoming negative. We call these charged particles ions.
Figure 1 (Left) shows how we draw the electrons on an ion. Again we use the dot and cross system. Use one symbol for the electrons that the element usually has, and another symbol for any extra electrons. (If the element has lost electrons, don’t worry about the second symbol!)
At GCSE we will only ever have to draw dot and cross diagrams for the first 20 elements