Formula from names of compounds
The chemical formula of a covalent molecular substance gives the number of atoms per molecule. The formula of a covalent network or ionic compound gives the simplest ratio of atoms/ions in the substance.
Sometimes the name of the compound gives information about the formula of that compound. Names of these compounds have prefixes that give the number of atoms of certain elements in each molecule.
| Prefix | Number of atoms |
| Mono- | One |
| Di- | Two |
| Tri- | Three |
| Tetra- | Four |
| Penta- | Five |
| Hexa- | Six |
| Prefix | Mono- |
|---|---|
| Number of atoms | One |
| Prefix | Di- |
|---|---|
| Number of atoms | Two |
| Prefix | Tri- |
|---|---|
| Number of atoms | Three |
| Prefix | Tetra- |
|---|---|
| Number of atoms | Four |
| Prefix | Penta- |
|---|---|
| Number of atoms | Five |
| Prefix | Hexa- |
|---|---|
| Number of atoms | Six |
For example, carbon monoxide contains one carbon atom joined to one oxygen atom, so it has the formula CO.
The ending of the name can also give information on the number of elements in a compound.
| Ending | Number of elements |
| -ide | Two |
| -ite | Three (one being Oxygen) |
| -ate | Three (one being Oxygen) |
| Ending | -ide |
|---|---|
| Number of elements | Two |
| Ending | -ite |
|---|---|
| Number of elements | Three (one being Oxygen) |
| Ending | -ate |
|---|---|
| Number of elements | Three (one being Oxygen) |