All substances are described by their formulae, which are used to write balanced chemical equations. Writing the formula for an ionic compound requires knowledge of the charges on its ions.
The chemical formula for a simple covalent molecule shows:
For example, the formula H2O shows that a water molecule contains two hydrogen atoms and one oxygen atom.
Useful formulae of simple covalent molecules:
| Compound | Formula |
|---|---|
| Water | H2O |
| Carbon dioxide | CO2 |
| Carbon monoxide | CO |
| Nitrogen dioxide | NO2 |
| Nitrogen monoxide | NO |
| Sulfur dioxide | SO2 |
| Methane | CH4 |