Rules for Naming Inorganic Compounds

IUPAC Rules for Inorganic Nomenclature

IONIC 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)

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-

Ionic 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

COVALENT COMPOUNDS

For covalent compounds involving metals, the above rules are still used when metals are involved:

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
N₂H₄	hydrazine
PH₃	phosphine
AsH₃	arsine
NO	nitric oxide
N₂O	nitrous oxide

Practice Quiz.Try to name the following compounds.

Compound Name ?

NaF

H₂S

K₂CO₃

FeCl₃

Mg(OH)₂

NH₄Br

PbI₂

Al₂O₃

CaS

CaSO₃

CaSO₄

Ca₃(PO₄)₂

Na₃N

Li₂O

K₂S

(NH₄)₂S

Fe₂O₃

Mg₃P₂

NaNO₃

SO₃

KCl

BaSO₄

ZnCl₂

AgNO₃

WO₃

CoCl₂

TiO

Answers

Compound Name

NaF Sodium Fluoride

H₂S Hydrogen Sulfide

K₂CO₃ Potassium Carbonate

FeCl₃ Iron(III) Chloride

Mg(OH)₂ Magnesium Hydroxide

NH₄Br Ammonium Bromide

PbI Lead(II) Iodide

Al₂O₃ Aluminum Oxide

CaS Calcium Sulfide

CaSO₃ Calcium Sulfite

CaSO₄ Calcium Sulfate

Ca₃(PO₄)₂ Calcium Phosphate

Na₃N Sodium Nitride

Li₂O Lithium Oxide

K₂S Potassium Sulfide

(NH₄)₂S Ammonium Sulfide

Fe₂O₃ Iron(III) Oxide

Mg₃P₂ Magnesium Phosphide

NaNO₃ Sodium Nitrate

SO₃ Sulfur Trioxide

KCl Potassium Chloride

BaSO₄ Barium Sulfate

ZnCl₂ Zinc Chloride

AgNO₃ Silver Nitrate

WO₃ Tungsten (VI) Oxide

CoCl₂ Cobalt (II) Chloride

TiO Titanium (II) Oxide