In chemical nomenclature, the IUPAC nomenclature of inorganic chemistry is a systematic method of naming inorganic chemical compounds, as recommended by the International Union of Pure and Applied Chemistry (IUPAC). It is published in Nomenclature of Inorganic Chemistry (which is informally called the Red Book).[1] Ideally, every inorganic compound should have a name from which an unambiguous formula can be determined. There is also an IUPAC nomenclature of organic chemistry.

The names "caffeine" and "3,7-dihydro-1,3,7-trimethyl-1H-purine-2,6-dione" both signify the same chemical. The systematic name encodes the structure and composition of the caffeine molecule in some detail, and provides an unambiguous reference to this compound, whereas the name "caffeine" just names it. These advantages make the systematic name far superior to the common name when absolute clarity and precision are required. However, for the sake of brevity, even professional chemists will use the non-systematic name almost all of the time, because caffeine is a well-known common chemical with a unique structure. Similarly, H2O is most often simply called water in English, though other chemical names do exist.
Single atom anions are named with an -ide suffix: for example, H− is hydride.

Compounds with a positive ion (cation): The name of the compound is simply the cation's name (usually the same as the element's), followed by the anion. For example, NaCl is sodium chloride, and CaF2 is calcium fluoride.
Cations which have taken on more than one positive charge are labeled with Roman numerals in parentheses. For example, Cu+ is copper(I), 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. For naming metal complexes see the page on complex (chemistry).

Oxyanions (polyatomic anions containing oxygen) are named with -ite or -ate, for a lesser or greater quantity of oxygen, respectively. For example, NO−
2 is nitrite, while NO−
3 is nitrate. If four oxyanions are possible, the prefixes hypo- and per- are used: hypochlorite is ClO−, perchlorate is ClO−
4.

The prefix bi- is a deprecated way of indicating the presence of a single hydrogen ion, as in "sodium bicarbonate" (NaHCO3). The modern method specifically names the hydrogen atom. Thus, NaHCO3 would be pronounced sodium hydrogen carbonate.
Positively charged ions are called cations and negatively charged ions are called anions. The cation is always named first. Ions can be metals, non-metals or polyatomic ions. Therefore, the name of the metal or positive polyatomic ion is followed by the name of the non-metal or negative polyatomic ion. The positive ion retains its element name whereas for a single non-metal anion the ending is changed to -ide.

Example: sodium chloride, potassium oxide, or calcium carbonate.
When the metal has more than one possible ionic charge or oxidation number the name becomes ambiguous. In these cases the oxidation number (the same as the charge) of the metal ion is represented by a Roman numeral in parentheses immediately following the metal ion name. For example, in uranium(VI) fluoride the oxidation number of uranium is 6. Another example is the iron oxides. FeO is iron(II) oxide and Fe2O3 is iron(III) oxide.

An older system used prefixes and suffixes to indicate the oxidation number, according to the following scheme:

Naming simple ionic compounds[edit]
An ionic compound is named by its cation followed by its anion. See polyatomic ion for a list of possible ions.
For cations that take on multiple charges, the charge is written using Roman numerals in parentheses immediately following the element name. For example, Cu(NO3)2 is copper(II) nitrate, because the charge of two nitrate ions (NO−
3) is 2 × −1 = −2, and since the net charge of the ionic compound must be zero, the Cu ion has a 2+ charge. This compound is therefore copper(II) nitrate. In the case of cations with a +4 oxidation state, the only acceptable format for the Roman numeral 4 is IV and not IIII.
The Roman numerals in fact show the oxidation number, but in simple ionic compounds (i.e., not metal complexes) this will always equal the ionic charge on the metal. For a simple overview see [1], for more details see selected pages from IUPAC rules for naming inorganic compounds.

List of common ion names[edit]
Monatomic anions:
Cl−
 chloride
S2−
 sulfide
P3−
 phosphide

Polyatomic ions:
NH+
4 ammonium
H
3O+
 hydronium
NO−
3 nitrate
NO−
2 nitrite
ClO−
 hypochlorite
ClO−
2 chlorite
ClO−
3 chlorate
ClO−
4 perchlorate
SO2−
3 sulfite
SO2−
4 sulfate
HSO−
3 hydrogen sulfite (or bisulfite)
HCO−
3 hydrogen carbonate (or bicarbonate)
CO2−
3 carbonate
PO3−
4 phosphate
HPO2−
4 hydrogen phosphate
H
2PO−
4 dihydrogen phosphate
CrO2−
4 chromate
Cr
2O2−
7 dichromate
BO3−
3 borate
AsO3−
4 arsenate
C
2O2−
4 oxalate
CN−
 cyanide
SCN−
 thiocyanate
MnO−
4 permanganate

Naming hydrates[edit]

Hydrates are ionic compounds that have absorbed water. They are named as the ionic compound followed by a numerical prefix and -hydrate. The numerical prefixes used are listed below (see IUPAC numerical multiplier):
mono-
di-
tri-
tetra-
penta-
hexa-
hepta-
octa-
nona-
deca-
For example, CuSO4·5H2O is "copper(II) sulfate pentahydrate".