As we have already learned, ionic bonding occurs between metals and non-metals. We now need to describe exactly how this type of bonding occurs, and represent ionic bonding using dot and cross diagrams.

In ionic bonding, the metal gives its outer electrons to the non-metal - electrons are transferred in this type of bonding.

The metal has lost electrons, and is now a positive ion or cation.

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The non-metal has gained electrons, and is now a negative ion or anion.

As the ions have opposite charges they will attract each other, and this attractive or electrostatic force is called an ionic bond.

Both the metal and non-metal now have full outer shells of electrons. The arrangement of electrons in the ions will be the same as a noble gas, and this is a very stable arrangement.

Dot and Cross Diagrams.

These diagrams are used to show how electrons have moved when elements bond together.
Electrons from one element are shown as dots, and electrons from one element are shown as crosses. It is important that you are aware that there is only one type of electron, and dots and crosses are only used to help our understanding.
To make dot and cross diagrams clearer, we normally only show the outer shells of electrons.

Example 1 - Sodium Chloride.

Example 2 - Magnesium Chloride.

Checkpoint.

Draw dot and cross diagrams for the following ionic compounds. State the charges on the metal and the non-metal ions, and write the chemical formula for the compound.

a. potassium fluoride.
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b. sodium oxide
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c. calcium bromide
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d. magnesium oxide.
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