Introduction: Imagine for a moment that you are a student in a supply closet, helping to get bottles of water for a school dance. It seems that your chemistry teacher has been storing some unused chemicals for the year in that supply closet, and some bottles are labeled [math]H_2O_2[/math]. If you weren't aware of how to name chemical compounds properly, you might accidentally bring bottle of what is known as hydrogen peroxide to the school dance, thinking that it's actually water, which is written as [math]H_2O[/math]. Unfortunately, someone drinking hydrogen peroxide would get incredibly sick. This is where chemical nomenclature, or the naming of chemical compounds in chemistry, comes in.

Chemical nomenclature is used to name compounds of all different kinds in chemistry. Nomenclature is especially important because, even though certain chemicals may contain the same elements, the amount of each type of element in different substances and mixtures can differ. For example, [math]Cu_2O[/math] has 2 copper atoms and 1 oxygen atom and is named copper (I) oxide, whereas CuO has 1 copper atom and 1 oxygen atom is named copper (II) oxide.

In naming ionic compounds like CuO, the name of the metal in the compound is followed by the ion name of the nonmetal. When the metal has more than one oxidation state, as is the case with transition metals, Roman numerals are used to indicate the specific oxidation state of the metal in the compound. Copper (I) oxide, for example, has a copper ion with a charge of +1, while copper (II) oxide has a copper ion with a charge of +2. In naming molecular (or covalent) compounds, on the other hand, the name of the first nonmetal has a prefix to indicate the number of atoms of that element, followed by the name of the second nonmetal with a prefix to indicate the number of atoms and the ending "-ide". For example, [math]N_2O_5[/math] would be named dinitrogen pentoxide, since there are two nitrogen atoms and five oxygen atoms.