Chemical Nomenclature

What is chemical nomenclature?

Chemical nomenclature is called a system of rules that allows different chemical compounds to be named according to the type and number of elements that compose them. The nomenclature allows to identify, classify and organize chemical compounds.

The purpose of chemical nomenclature is to assign chemical names and formulas, also called descriptors, to chemical substances in such a way that they are easily recognizable and a convention can be established.

Within the chemical nomenclature, two large groups of compounds are distinguished:

  • organic compoundsreferring to those with the presence of carbon bonded with molecules of hydrogen, oxygen, sulfur, nitrogen, boron and certain halogens;
  • inorganic compoundswhich refer to the entire universe of chemical compounds that do not include carbon molecules.

The main institution in charge of regulating or establishing the conventions is the International Union of Pure and Applied Chemistry or IUPAC for its acronym in English (International Union of Pure and Applied Chemistry).

Types of chemical nomenclature

There are three systems of chemical nomenclature:

  • Traditional, functional or classic nomenclature system.
  • Systematic or stoichiometric nomenclature system.
  • Stock nomenclature system.

Depending on the nomenclature system used, the same compound can receive different names. For example, SnOtwo may be called tin dioxide (traditional nomenclature), tin(IV) oxide (Stock nomenclature), and stannic oxide (stoichiometric nomenclature).

Functional or classic or traditional nomenclature system

Chemical substances are classified according to the different valences they possess. These are represented verbally with the use of prefixes and suffixes.

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Val No. Prefixes and suffixes examples
1 Use the connector “de” or the suffix -ico KtwoO, potassium oxide or potassium oxide

-bear (minor valence);

-ico (major valence)

FeO, ferrous oxide

FaithtwoEITHER3iron oxide


hiccup + name + bear (minor valence)

-bear (val. intermedia)

-ico (major value)

SO, hyposulfurous oxide

SWtwosulphurous oxide

SW3sulfuric oxide


hiccup + name + bear (smallest value)

-bear (val. small)

-ico (intermediate value)

per + name + ico (big value)

CltwoO, hypochlorous oxide

CltwoEITHER3chlorous oxide

CltwoEITHER5chloric oxide

CltwoEITHER7perchloric oxide

Stoichiometric or systematic nomenclature system

This is the most widespread today and is recognized by the IUPAC. Name substances with Greek number prefixes. These indicate the atomicity (number of atoms) present in the molecules. The formula for naming compounds can be summarized as follows: generic name-prefix + specific name-prefix. We can see the following table to guide us.

Att. No. C Prefix examples
1 met- or mono-

CH4, methane;

CO, carbon monoxide

two et- or di- COtwo, carbon dioxide
3 prop- or tri-

C3H8, propane

CrBr3chromium tribromide

4 but- or tetra-


Cl4C, carbon tetrachloride

5 penta-


NtwoEITHER5dinitrogen pentoxide

6 hexa- C6H14hexane
7 hepta-


CltwoEITHER7dichloro heptoxide

8 octa- C8H18octane
9 non-, nona- or eneá- C9Htwentynonane
10 deca- C10H22 dean

Stock Nomenclature System

Currently, the IUPAC is promoting the standardization of this method instead of those that use suffixes, because suffixes are difficult in some languages. The chosen system is called Stock. It gets its name from its creator, the German chemist Alfred Stock (1876-1946).

The Stock system adds Roman numerals to the end of the element to indicate the valence of the atoms. That is, the Roman numerals indicate the oxidation state of any of the elements that may be present in the chemical substance. They must be placed at the end of the name of the substance and between parentheses.

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For example:

No. valences Nomenclature
two HtwoS, Hydrogen(II) Sulfide
two FeO, iron(II) oxide
two Mg(Br)2: Bromide sw magnesium (II)
4 SO3, sulfur oxide (IV)

See also:

  • organic compounds
  • inorganic compounds
  • organic chemistry
  • Inorganic chemistry