Binary covalent compounds are compounds made up of only two elements, such as carbon dioxide. Prefixes are used in the names of binary compounds to indicate the number of atoms of each nonmetal present.

The following table lists the most common prefixes for binary covalent compounds.

Common Prefixes for Binary Covalent Compounds
Number of Atoms Prefix
1 mono-
2 di-
3 tri-
4 tetra-
5 penta-
6 hexa-
7 hepta-
8 octa-
9 nona-
10 deca-

In general, the prefix mono- is rarely used. Carbon monoxide is one of the few compounds that uses this prefix.

Take a look at the following examples to see how to use the prefixes when naming binary covalent compounds (the prefixes appear in bold). Note that chemists try to avoid putting an a and an o together with the oxide name, as in decaoxide, so they normally drop the a off the prefix.

carbon dioxide:


tetraphosphorus decoxide:


sulfur trioxide:


dinitrogen tetroxide:


This naming system is used only with binary, nonmetal compounds, with one exception. The following compound is commonly called manganese dioxide.