Key learning points

1. Dot and cross diagrams as a model for binary ionic substances
2. Dot and cross diagrams show the empirical formula/ratio of atoms to show how electrons are transferred
3. Ions are shown with full outer shells, square brackets, and a charge in the top right corner.
4. Ionic compounds are neutral overall, so positive and negative charge must balance.
5. When positive ions do not have the same magnitude of charge as negative ions, multiple of some ions will be required.

Keywords

• Binary ionic substance - is made up of two different elements, one of which is a metal and the other a non-metal element.

• Empirical formula - show the simplest whole number ratio of atoms of each element in a compound.

• Ratio - can be used to determine the size of one quantity in relation to another.

• Dot-and-cross diagram - is used to show how chemical bonds are formed between atoms. The electrons from one atom are shown as dots and the electrons from the other atom are shown as crosses.

• Magnitude - is the size of a quantity, for example the size of the charge on the ion.

Common misconception