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Created: 11 Aug, 2010; Last Modified: 07 Sep, 2010

The Language of Chemistry - 05

Chemical Nomenclature

Table 1: Prefixes used in naming binary covalent compounds.(Adapted from: Bishop, Introduction Chemistry, p. 91)
No. of atoms Prefix for 1st element Prefix for 2nd element
1 -- mon(o)
2 di di
3 tri tri
4 tetra tetr(a)
5 penta pent(a)
6 hexa hex(a)
7 hepta hept(a)
8 octa oct(a)
9 nona non(a)
10 deca dec(a)

Chemical nomenclature is the scientific method of naming compounds systematically. In the previous centuries, chemical compounds were being named in an ad-hoc manner, till finally it dawned that a naming system was needed to bring some order into the chaos.

Today, under the guidance of IUPAC (International Union of Pure and Applied Chemistry), chemistry follows a more-or-less systematic naming system. The goal of chemical nomenclature is to identify each chemical compound uniquely through a systematic naming system, and to also convey extra information about the very structure of the compound from the name itself.

Binary Compounds

Table 2: Roots of names of non-metals.(Adapted from: Bishop, Introduction Chemistry, p. 92)
Element Root for 2nd element
C carb
N nitr
P phosph
O ox
S sulph
F fluor
Cl chlor
Br brom
I iod

Binary compounds are made up of two elements.

Binary covalent compounds

Some binary covalent compounds are still identified by names that they have been known by for years, such as water (H2O) and ammonia (NH3), but most are now systematically named. Binary covalent compounds consists of two non-metallic elements of the form AxBy, where A and B are non-metals, and x and y are subscripts (absence of subscript denotes 1).

There are two tables which are useful for naming purposes.

  • Table – table of prefixes used for naming the binary covalent compounds.
  • Table – table of roots for names of the non-metal elements.
Table 3: Roots of names of anions.(Adapted from: Bishop, Introduction Chemistry, p. 98)
Anion Root for 2nd element
N3- nitr
P3- phosph
O2- ox
S2- sulph
H- hydr
F- fluor
Cl- chlor
Br- brom
I- iod

Here's how the naming process works for binary covalent compounds, taking AxBy as the format, and N2O5 as an example:

  1. If x > 1, the associated prefix for the first element from Table is attached to the name of A. (For x = 1, mono is not used at the beginning of the compound's name).
    Thus, the N2 portion of N2O5 will be indicated as dinitrogen.
  2. For all y (even if y = 1), select the prefix from Table for the second element. If the B's name begins with a vowel, leave the ";a" off the end of the prefixes that end in "a" and "o" off "mono". In this case, B's name (oxygen) does begin with a vowel, and the prefix "penta" does end in "a".
    The name for N2O5 now develops to dinitrogen pent-.
  3. Using Table , attach the root of the name of the second element B to the developing name.
    The name for N2O5 now develops to dinitrogen pentox-.
  4. Add -ide to the end of the name.
    The name for N2O5 is dinitrogen pentoxide.
Table 4: Roots of names of hydracids.
Anion Root for 2nd element
F- fluor
Cl- chlor
Br- brom
I- iod
S2- sulphur
Binary hydrogen compounds (non acids)

When naming hydrogen based binary covalent compounds which are not acids, the prefixes need not be used. Thus,

  • HCl is hydrogen chloride or hydrogen monochloride
  • H2S is hydrogen sulphide or dihydrogen monosulphide.

Binary ionic compounds

Binary ionic compounds consists of a metal and a non-metal element, and is of the form MxNy, where M is a metal (cation) and N is a non-metal (anion), and x and y are subscripts (absence of subscript denotes 1).

Table 5: Names of some polyatomic ions.
Radical Name
NH4+ ammonium
CH3COO- acetate
HCO3- bicarbonate (hydrogencarbonate)
HSO4- bisulphate (hydrogensulphate)
HSO3- bisulphite (hydrogensulphite)
CO32- carbonate
ClO3- chlorate
ClO2- chlorite
CrO42- chromate
CN- cyanide
Cr2O72- dichromate
Fe(CN)63- ferricyanide
Fe(CN)64- ferrocyanide
OH- hydroxide
ClO- hypochlorite
NO3- nitrate
NO2- nitrite
ClO4- perchlorate
Mn4- permanganate
O22- peroxide
PO43- phosphate
PO33- phosphite
Si4O32- silicate
SO42- sulphate
SO32- sulphite

The first part of the name is the name of cation (i.e. the metal's name), while the root of the second part is derived from Table (which is very similar to Table ) and then suffixed with -ide.

Thus, we have calcium fluoride for CaF2 and aluminium oxide for Al2O3.

Binary acids (Hydracids)

A binary acid (hydracid) contains hydrogen and another non-metal. The names of hydracids begins with hydro- as the first part, followed by the root of the second element as derived from Table , and ends with –ic acid. However, when the root name begins with a vowel, the first part is hydr-, as in the case of hydriodic acid (HI).

Ternary Compounds

Ternary compounds have three or more elements, one of which is usually oxygen.

Ionic compounds with polyatomic ions

Metal cation – Polyatomic anion

In this case, the first part is the name of the metal (cation), and the second part is the name of the polyatomic anion (see Table ). So, CaCO3 is calcium carbonate, and Fe2(SO4)3 is iron(III) sulphate.

Polyatomic cation – non-metal anion

The first part is the name of the polyatomic cation, the second part is named with the help of Table just as in the case for for non-metal anions in binary ionic compounds. Thus, NH4Cl is ammonium chloride.

Table 6: Names of some oxoanions which form oxoacids.
Oxoanion Name
CH3COO- acetate
HCO3- bicarbonate (hydrogencarbonate)
HSO4- bisulphate (hydrogensulphate)
HSO3- bisulphite (hydrogensulphite)
CO32- carbonate
ClO3- chlorate
ClO2- chlorite
CrO42- chromate
ClO- hypochlorite
NO3- nitrate
NO2- nitrite
ClO4- perchlorate
PO43- phosphate
PO33- phosphite
Si4O32- silicate
SO42- sulphate
SO32- sulphite
Polyatomic cation – polyatomic anion

The first part is the name of the polyatomic cation, and the second part is the name of the polyatomic anion. An example is (NH4)2SO4 which is ammonium sulphate.

Oxoacids (Oxyacids)

Oxoacids, or oxyacids, in addition to hydrogen, contains an oxoanion. which is a polyatomic anion containing oxygen.

A list of oxoanions is given in Table , which is a subset of Table , having only those radicals which have oxygen as a component.

The name of an oxoacid begins with the name of the oxoanion, with the -ite or -ate ending of the oxoanion substituted with -ous acid or -ic acid respectively.

Thus we have oxoacid names like nitric acid, HNO3, (from nitrate oxoanion NO3-) and sulphurous acid, H2SO3, (from sulphite oxoanion SO32-).

Bases (alkalis)

Bases or alkalis are simple to name. The first part is the name of the cation, while the second part is hydroxide. So we have names like sodium hydroxide (NaOH) and ammonium hydroxide (NH4OH).

Feedback

List of References

Bishop, M, An Introduction to Chemistry (First Version), viewed 10 February 2007 <http://preparatorychemistry.com/Bishop_Chemistry_First.htm>, 2005.

Bibliography

Bishop, M, An Introduction to Chemistry (First Version), viewed 10 February 2007 <http://preparatorychemistry.com/Bishop_Chemistry_First.htm>, 2005.
McMurray, J & Fay, RC, Chemistry, 4th edn, USA: Prentice Hall, 2003.
Mustoe, F et al, Chemistry 11, Canada:McGraw-Hill Reyerson, 2005.
Wikipedia contributors, 'IUPAC Nomenclature,' Wikipedia, The Free Encyclopedia, viewed 07 August, 2010 <http://en.wikipedia.org/wiki/IUPAC_nomenclature>, 2010.