Overview of nomenclature

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Nomenclature is a system that allows us to name compounds with different names so they can be easily identified as separate chemicals. Inorganic compounds are compounds that do not deal with the formation of Carbon and Hydrogen, or simply all other compounds that do not fit into the description of an organic compound.


Generally, there are two types of compounds that can be formed.

Compounds between Metals and Nonmetals (Cation and Anion)

This is commonly known as anIonic Compound,where the compound name has an ending of-ide.The net charge of any ionic compound must be zero which also means it must be electrically neutral. For example, one Na+is paired with one Cl-; one Ca2+is paired with two Br-. There are two rules that must be followed through:

  • Thecation(metal) is always named first with its name unchanged
  • Theanion(nonmetal) is written after the cation, modified to end in-ide

Na+ Cl- = NaCl

Sodium Chlorine SodiumChloride

Ca2+2Br- = CaBr2

Calcium Bromine CalciumBromide

The transition metals may form more than one ion, thus we need to specify which particular ion we are talking about. We indicate this by assigning a Roman numeral number after the metal. Iron can form two common ions, Fe2+and Fe3+. To indicate the difference, Fe2+would be named iron (II) and Fe3+would be named iron (III). The Roman numeral also tells us an extra bit of information, the number assigned is the oxidation state or the charge of that ion.

FeCl2 FeCl3

Iron (II)Chloride Iron (III)Chloride

Several exceptions apply to the Roman numeral assignment: Aluminum, Zinc, and Silver. Although they belong to the transition metal category, Roman numerals are not written after the metal name because those three metals only exist in one ion.

  • AluminumAl3+
  • ZincZn2+
  • SilverAg1+

Instead of using Roman numerals, the different ions can also be presented in plain words. The metal is changed to end in-ousor-ic.

  • ousending is used for theloweroxidation state
  • icending is used for thehigheroxidation state

Cu2O CuO

Charge of copper is +1 Charge of copper is +2

CuprousOxide CupricOxide

FeCl2 FeCl3

Charge of iron is +2 Charge of iron is +3

FerrousChloride FerricChloride

However, this -ous/-ic system is inadequate in some cases, so the Roman numeral system is preferred. This system is used commonly in naming acids, where H2SO4is commonly known as Sulfuric Acid, and H2SO3is known as Sulfurous Acid.

Compounds between Nonmetals and Nonmetals (Anion and Anion)

This is commonly known as aMolecular Compound, where the element with the positive oxidation state is written first.In many cases, nonmetals form more than one binary compound, soprefixesare used to distinguish them.

# of Atoms Prefixes

  1. Mono-
  2. Di-
  3. Tri-
  4. Tetra-
  5. Penta-
  6. Hexa-
  7. Hepta-
  8. Octa-
  9. Nona-
  10. Deca-

CO = carbonmonoxide BCl3= borontrichloride

CO2= carbondioxide N2O5=dinitrogenpentoxide

The prefixmono-is treated so that it is not used for the first element. If there isn't a prefix before the first element, it is assumed that there is only one of that element.

Binary Acids

Although HF can be named hydrogen fluoride, often acids are given a different name for emphasis that it is an acid. An acid is a substance that dissociates into hydrogen ions (H+) and anionsin water. To name acids, the prefixhydro-is placed in front of the nonmetal modified to end with-ic.

Some common binary acids include:

HF (aq) =hydrofluoricacidHF (g) = hydrogen fluoride

HBr (aq) =hydrobromicacidHBr (g) = hydrogen bromide

HCl (aq) =hydrochloricacidHCl (g) = hydrogen chloride

H2S (aq) =hydrosulfuricacid H2S (g) = hydrogen sulfide

It is very important to include (aq) after the acids, because as the same compounds are written in gas phase, hydrogen is named first, followed by the anion ending with-ide.

Polyatomic Ions

Inpolyatomic ions, two or more atoms are joined together by covalent bonds. Polyatomic anions are more common than polyatomic cations as shown in the chart below.

Increasing oxidation state of the nonmetalà


Increasing number of oxygen atomsà

(Usage of this example can be seen from the set of compounds containing Cl and O)

Common Polyatomic ions

Name : Formula

Ammonium ion NH4+

Acetate ion C2H3O2-

Carbonate ion CO32-

Hypochlorite ion ClO-

Chlorite ion ClO2-

Chlorate ion ClO3-

Perchlorate ion ClO4-

Chromate ion CrO42-

Dichromate ion Cr2O72-

Cyanide ion CN-

Hydroxide ion OH-

Nitrite ion NO2-

Nitrate ion NO3-

Oxalate ion C2O42-

Permanganate ion MnO4-

Phosphate ion PO43-

Sulfite ion SO32-

Sulfate ion SO42-

Thiosulfate ion S2O32-

Outside links

  • http://www.mikeblaber.org/oldwine/chm1045/notes/Atoms/Naming/Atoms06.htm
  • http://en.wikipedia.org/wiki/IUPAC_nomenclature_of_inorganic_chemistry
  • http://chemistry.boisestate.edu/people/richardbanks/inorganic/NamingInorganicCompoundsC101.html

Games to learn nomenclature!

  • http://www.sciencegeek.net/Chemistry/taters/ions/page1.htm
  • http://misterguch.brinkster.net/ioniccovalentworksheets.html
  • http://www.studystack.com/matching-10327


  1. Pettrucci, Ralph H.General Chemistry:Principles and Modern Applications. 9th. Upper Saddle River:Pearson Prentice Hall, 2007
  2. Nomenclature of Inorganic Chemistry, Recommendations 1990, Oxford:Blackwell Scientific Publications. (1990)
  3. International Union of Pure and Applied Chemistry(2005).Nomenclature of Inorganic Chemistry(IUPAC Recommendations 2005). Cambridge (UK):RSC-IUPAC.ISBN 0-85404-438-8.Electronic version..
  4. Biochemical Nomenclature and Related Documents, London:Portland Press, 1992.

Outside Links

  • Link to outside sources. Wikipedia entried should probably be referenced here.


  1. What is the correct formula for Calcium Carbonate?
  2. a.Ca+CO2-

  3. What is the correct name for FeO?
  4. a.Iron oxide
    b.Iron dioxide
    c.Iron (III) oxide
    d.Iron (II) oxide

  5. What is the correct name for Al(NO3)3?
  6. a.Aluminum nitrate
    b.Aluminum (III) nitrate
    c.Aluminum nitrite
    d.Aluminum nitrogen trioxide

  7. What is the correct formula of phosphorus trichloride?
  8. a.P2Cl2

  9. What is the correct formula of lithium perchlorate?
  10. a.Li2ClO4
    d.None of these

    Answer Key: 1.C2.D3.A4.B5.D, LiClO4