Exceptions to Note when Naming Molecular Compounds

If there is only one atom of the first element, the prefix mono- is normally omitted.

CO2 mono carbon    di-    ox    -ide

The full name is carbon dioxide.

The compound N2O (also called laughing gas) is named according to the first element, nitrogen, with the prefix di-, followed by the base name of the second element, ox, prefixed by mono-, and the suffix -ide.

Since mono- ends with a vowel and oxide begins with a vowel, an o is dropped and the two are combined as monoxide.

The entire name is dinitrogen monoxide.

When the prefix ends with a vowel and the base name starts with a vowel, the first vowel is sometimes dropped.

Vowel is dropped in monoxide but not in dioxide or triiodide.