Drawing Ions

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.

Figure 1 A Chloride ion Note the square brackets to show what is charged and the numerical charge on the top right of the square brackets.

Figure 1
A Chloride ion
Note the square brackets to show what is charged and the numerical charge on the top right of the square brackets.

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

Figure 2 A Magnesium ion We can work this out because of the number of electrons and the charge on the ion. It shows that it had 2 more electrons than it does now.

Figure 2
A Magnesium ion
We can work this out because of the number of electrons and the charge on the ion. It shows that it had 2 more electrons than it does now.