Rules for Naming Inorganic Compounds

By Dr. Donald G. McGahan
Published: September 15, 2008
Modified: March 11, 2016

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Positive Ions (cations)

Monatomic positive ions take the names of the metal from which they are derived:

Ion Name
Na+ sodium ion
Ca2+ calcium ion
Al3+ aluminum ion

When a metal forms more than one ion, it is necessary to distinguish between these ions. The accepted practice today is to indicate the charge of the ion by a roman numeral in parenthesis immediately following the name of the metal:

Ion Name
Fe2+ iron(II)
Fe3+ iron(III)
Cu+ copper(I)
Cu2+ copper(II)
Sn2+ tin(II)
Sn4+ tin(IV)

Some metals are still referred to using the stem of their Latin name, with -ous and -ic indicating the lower and higher charges, respectively:

Ion Name
Fe2+ ferrous
Fe3+ ferric
Cu+ cuprous
Cu2+ cupric
Sn2+ stannous
Sn4+ stannic

The only common inorganic polyatomic positive ions are:

Ion Name
NH4+ ammonium
Hg22+ mercury(II) or mercurous

Negative Ions (anions)

Monatomic negative ions are named by adding the suffix -ide to the stem of the name of the nonmetal from which they are derived:

Ion Name
H hydride
F fluoride
Cl chloride
Br bromide
I iodide
O2- oxide
S2- sulfide
Se2- selenide
Te2- telluride
N3- nitride
P3- phosphide
C4- carbide

The nomenclature of polyatomic anions is more complex. The names of the most common are:

Ion Formula
borate BO33-
carbonate CO32-
hydrogen carbonate (bicarbonate) HCO3
hypochlorite ClO
chlorite ClO2
chlorate ClO3
perchlorate ClO4
chromate CrO42-
dichromate Cr2O72-
cyanide CN
phosphite PO33-
phosphate PO43-
hydrogen phosphate HPO42-
dihydrogen phosphate H2PO4
hydrogen sulfite (bisulfite) HSO3
hydrogen sulfate (bisulfate) HSO4
sulfite SO32-
sulfate SO42-
sulfide S2-
hydrosulfide HS
hydroxide OH
nitrite NO2
nitrate NO3
oxalate C2O42-
permanganate MnO4
silicate SiO44-


For ionic compounds, the name of the positive ion (cation) is given first, followed by the name of the negative ion (anion):

Compound Name
CaCl2 calcium chloride
Fe(ClO4)3 iron(III) perchlorate
FeBr2 iron(II) bromide
NaHCO3 sodium hydrogen carbonate
(NH4)2SO4 ammonium sulfate

For covalent compounds involving metals, the above practices are still used:

AlCl3 aluminum chloride
SnCl4 tin(IV) chloride

For compounds made up of nonmetals, the first element named is the one with lower electronegativity, with the second having the higher electronegativity:

Compound Name
HCl hydrogen chloride
H2S hydrogen sulfide
NF3 nitrogen fluoride

If more than one binary compound is formed by a pair of nonmetals, the Greek prefixes di (two), tri (three), tetra (four), penta (five), hexa (six),
etc. are used to designate the number of atoms present. The mono- prefix is rarely used.

Compound Name
N2O5 dinitrogen pentoxide*
N2O4 dinitrogen tetroxide
N2O3 dinitrogen trioxide
N2O2 dinitrogen dioxide
N2O dinitrogen oxide
NO2 nitrogen dioxide
NO nitrogen oxide

*when immediately followed by a vowel, the a is dropped.

Many of the most common binary nonmetal componds have common names which are use more frequently:

Compound Name
H2O water
H2O2 hydrogen peroxide
NH3 ammonia
N2H2 hydrazine
PH3 phosphine
AsH3 arsine
NO nitric oxide
N2O nitrous oxide


The names of inorganic oxyacids (those that contain oxygen) are derived from the names of the polyatomic
ions, replacing -ite with -ous, and -ate with -ic:

HClO hypochlorous acid HClO2 chlorous acid
HClO3 chloric acid HClO4 perchloric acid
HNO2 nitrous acid HNO3 nitric acid
H2SO3 sulfurous acid H2SO4 sulfuric acid
H3PO3 phosphorous acid H3PO4 phosphoric acid
H2CO3 carbonic acid H2CrO4 chromic acid
H2C2O4 oxalic acid H3BO3 boric acid
HMnO4 permanganic acid H4SiO4 silicic acid

Other common acids include*:

HCl hydrochloric acid HF hydrofluoric acid
HI hydroiodic acid HBr hydrobromic acid

*Acids which do not contain oxygen derive their name from the nonmetal ion or polyatomic ion with a hydro-
prefix. The -ide suffix for the anion is replaced with -ic.

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