The primary function of chemical nomenclature is to ensure that a spoken or written chemical name leaves no ambiguity concerning to what chemical compound the name refers. Each chemical name should refer to a single substance. Today, scientists often refer to chemicals by their common names, but it is important to be able to recognize and name all chemicals in a standardized way. The most widely accepted format for nomenclature has been established by IUPAC(Figure 2) as follows:
- Single atom anions are named with an -ide suffix. For example, H− is hydride.
- If a compound has a cation (that is, a positive ion), the name of the compound is the cation's name (which is usually the same as the element's name), followed by the anion. For example, NaCl is sodium chloride.
- Cations that are able to take on more than one positive charge are labeled with Roman numerals in parentheses. For example, Cu+ is copper(I), and Cu2+ is copper(II). An older, deprecated notation is to append -ous or -ic to the root of the Latin name to name ions with a lesser or greater charge. Under this naming convention, Cu+ is cuprous and Cu2+ is cupric.
- Oxyanions (which are polyatomic anions containing oxygen) are name with -ite and -ate for a lesser or greater quantity of oxygen, respectively. For example, NO2− is nitrite, while NO3− is nitrate. If four oxyanions are possible, the prefixes hypo- and per- are used; hypochlorite is ClO−, perchlorate is ClO4-.
- The prefix bi- is a deprecated way of indicating the presence of a single hydrogen ion. Using this method, NaHCO3 is sodium bicarbonate. The modern method specifically names the hydrogen atom; thus, NaHCO3 would be pronounced sodium hydrogen carbonate.
- Prefixes are used to dictate the number of a given element present. "di-" indicates two (sulfur dioxide has two oxygens), "tri-" is three, "tetra-" is four, "penta-" is five, and "hexa-" is six.
Inorganic molecular compounds are named with these prefixes before each element, signifying the quantity of each atom in the compound.(Figure 1) Generally the more electropositive atom is written first, followed by the more electronegative atom with an appropriate suffix. For example, H2O (water) can be called dihydrogen monoxide. Organic molecules do not follow this rule. In addition, the prefix mono- is not used with the first element; for example, SO2 is sulfur dioxide, not "monosulfur dioxide". Sometimes prefixes are shortened when the ending vowel of the prefix "conflicts" with a starting vowel in the compound. This makes the name easier to pronounce; for example, CO is carbon monoxide (as opposed to "monooxide").