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Naming of inorganic binary compounds

Rules for naming inorganic ionic and covalent types of chemical compounds

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See also Naming of Organic Compounds

Ionic compounds

Binary ionic compounds contain a positiv ion (cation) and a negative ion (anion). The cation is a metal in most cases, and is always written first in the formula. The anion is a nonmetal in most cases.

In the naming, these rules must be followed:

  1. The cation is always named first and the anion second.
  2. A cation takes its name from the name of the element.  Example: K+ is called potassium in the names of compounds containing this ion.
  3. An anion is named by taking the first part of the element name and adding -ide.  Example: the Br- ion is called bromide.

A monatomic ion is an ion consisting of a single atom. Examples are given in the table:

Monatomic cations and anions
Cation Name Anion Name
Al3+ Aluminium Br- Bromide
Ba2+ Barium Cl- Chloride
Be2+ Beryllium F- Fluoride
Ca2+ Calcium H- Hydride
Cs+ Cesium I- Iodide
H+ Hydrogen N3- Nitride
Li+ Lithium O2- Oxide
Mg2+ Magnesium P3- Phosphide
K+ Potassium S2- Sulfide
Rb+ Rubidium
Ag+ Silver
Na+ Sodium
Sr2+ Strontium
Zn2+ Zinc

A polyatomic ion contains more than one atom, these atoms can be of the same element or of different elements.

There are polyatomic anion series with one given element together with different numbers of oxygen atoms, called oxyanions:

  1. In oxyanion series with two members, the name of the one with the smaller number of oxygen atoms ends in -ite.
  2. The name of the one with the larger number ends in -ate.
  3. When more than two oxyanions make up a series,
    • hypo- (less than) are used as prefix to name the member of the series with the fewest oxygen atoms.
    • per- (more than) are used as prefix to name the member of the series with the most oxygen atoms.
Polyatomic ions
Ion Name Ion Name
NH4+ Ammonium MnO4- Permanganate
C2H3O2- Acetate NO2- Nitrite
CO32- Carbonate NO3- Nitrate
HCO3- Hydrogen carbonate (or bicarbonate) OH- Hydroxide
ClO- Hypochlorite O22- Peroxide
ClO2- Chlorite PO43- Phosphate
ClO3- Chlorate HPO42- Hydrogen phosphate
ClO4- Perchlorate H2PO42- Dihydrogen phosphate
CN- Cyanide SO32- Sulfite
CrO42- Chromate SO42- Sulfate
Cr2O7- Dichromate HSO4- Hydrogen sulfate (or bisulfate)

Type I binary ionic compounds contains a metal that forms only one type of cation. Examples:  Na+ and Ca2+ . Examples of naming of compounds type I is given in the table:

Type I compounds, naming examples
Compound Ions present Name
CaS Ca2+,  S2- Calcium sulfide
CsBr Cs+,   Br- Cesium bromide
Li3N Li+,   N3- Lithium nitride
MgO Mg2+,  O2- Magnesium oxide
KF K+,   F- Potassium fluoride
AgI Ag+,   I- Silver iodide
NaCl Na+,   Cl- Sodium chloride

Type II binary ionic compounds can form more than one type of cation.  Examples: Fe2+ and Fe3+,  Pb2+ and Pb4+.

For type II compounds the charge of the metal ion must be specified, and this is systematically done with Roman numeral indication.

Example:  iron(II) for Fe2+ and iron(III) for Fe3+.  Then, the compounds with formula FeCl2 and FeCl3 are called iron(II) chloride and iron(III) chloride, respectively.

An older way to separate between metal ions that forms two different charges:

The ion with the lower charge has a name ending in -ous and the one with the higher charge has a name ending in -ic. 

Type II cations
Ion Systematic name Alternate name
Co2+ Cobalt(II) Cobaltous
Co3+ Cobalt(III) Cobaltic
Cu+ Copper(I) Cuprous
Cu2+ Copper(II) Cupric
Fe2+ Iron(II) Ferrous
Fe3+ Iron(III) Ferric
Pb2+ Lead(II) Plumbous
Pb4+ Lead(IV) Plumbic
Hg+ Mercury(I) Mercurous
Hg22+* Mercury(II) Mercuric
Sn2+ Tin(II) Stannous
Sn4+ Tin(IV) Stannic

Covalent compounds (contain two nonmetals)

Rules for naming binary covalent compounds:

Nonmetal X + Nonmetal Y + "-ide"

  1. The first element in the formula is named first, using the full element name
  2. The second element is named as if it were an anion.
  3. Prefixes are used to denote the numbers of atoms present (mono-, di-, tri-, tetra-, penta-, hexa-, hepta-, octa-)
  4. The prefix mono- is never used for naming the first element. Example: CO is called carbon monoxide (not monocarbon monoxide).
  5. Some elements beginning with vowels (Oxygen, for example) replace the vowel ending -o or -a of its prefix; mono- + Oxide = Monoxide, O4 = Tetroxide, O5 = Pentoxide, and so on.
Examples of naming covalent compounds with nitrogen and oxygen
Compound Systematic name Common name
NO Nitrogen monoxide Nitric oxide
NO2 Nitrogen dioxide
N2O Dinitrogen monoxide Nitrous oxide
N2O3 Dinitrogen trioxide
N2O4 Dinitrogen tetroxide
N2O5 Dinitrogen pentoxide

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