Chemical Reactions: Bonding Writing Chemical Formulae: Ionic Compounds
To predict the chemical formula of ionic compounds, you first need to find out the charge on an ion using the periodic table.
Using the periodic table to predict what ions are formed
Using the example as a guide, write out the electronic configurations for the atoms listed below. Use the configurations to predict the type of ion (positive or negative) that the atom will form.
Example: Electronic configurations of sodium: 2, 8, 1 It will lose 1 electron and become [2, 8]+1 Sodium ion = Na+1
zz zz zz zz
Group 1: Lithium and potassium Group 2: Magnesium and calcium Group 6: Oxygen and sulfur Group 7: Fluorine and bromine
Can you spot a trend that connects the periodic table to the ions formed by the atoms of the elements?
The periodic table can be used in constructing the chemical formulae for compounds that form between metals and non-metals.
Naming compounds
When naming a compound formed between a metal and a non-metal: zz
The name of the metal always comes first.
The name of the non-metal follows and its ending is changed to ‘–ide’. For example, sodium and chlorine combine to make sodium chloride.
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A compound is always neutral. This means the charges of the ions in the compound must balance.
When writing the chemical formula for an ionic compound, you need to work out the correct ratio of ions that will give an overall neutral charge for the compound.
Look at the following two examples of how to use the periodic table to work out chemical formulae for ionic compounds.
