Rules for Naming Inorganic Compounds

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
O^2-	oxide
S^2-	sulfide
Se^2-	selenide
Te^2-	telluride
N^3-	nitride
P^3-	phosphide
C^4-	carbide

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

Ion	Formula
borate	BO₃^3-
carbonate	CO₃^2-
hydrogen carbonate (bicarbonate)	HCO₃^-
hypochlorite	ClO^-
chlorite	ClO₂^-
chlorate	ClO₃^-
perchlorate	ClO₄^-
chromate	CrO₄^2-
dichromate	Cr₂O₇^2-
cyanide	CN^-
phosphite	PO₃^3-
phosphate	PO₄^3-
hydrogen phosphate	HPO₄^2-
dihydrogen phosphate	H₂PO₄^-
hydrogen sulfite (bisulfite)	HSO₃^-
hydrogen sulfate (bisulfate)	HSO₄^-
sulfite	SO₃^2-
sulfate	SO₄^2-
sulfide	S^2-
hydrosulfide	HS^-
hydroxide	OH^-
nitrite	NO₂^-
nitrate	NO₃^-
oxalate	C₂O₄^2-
permanganate	MnO₄^-
silicate	SiO₄^4-

Compounds

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

Acids

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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