Chemistry 141
Fall 2003
General guidelines for nomenclature
Chemical nomenclature is the process of giving unambiguous (clear) chemical formulas
or chemical names for elements and compounds. Since there are so many elements (118
now) and compounds (hundreds of millions), it is quite important for everybody to be on
the same page and provide a clear and unmistakable name for the element or compound
in question.
In the early beginnings of scientific literature it was fairly common to have multiple
names for the same element/compound, which led to nothing but confusion and
arguments. For example the compound CuSO4 was called Blue Vitriol, which conveyed
no information about the type or the number of the elements that made up this compound.
According to modern naming methods this compound is called Copper sulfate, which
tells us that it is made of copper and sulfate ions.
Nowadays the rules for writing the names of chemicals and writing chemical formulas
have been set by the Nomenclature Committee of the International Union of Pure and
Applied Chemistry (IUPAC). The older names are still used and are called common
names. Thus “soda ash” is a common name for Na2CO3 and sodium carbonate is the
complete IUPAC name. In this class you will occasionally come across a common name
like water (H2O), but otherwise we will follow the IUPAC rules for nomenclature.
In this class you will be expected to learn and be able to use the IUPAC rules of
nomenclature for five different broad classes of compounds; binary compounds (both
metal-nonmetal and nonmetal-nonmetal), metal-polyatomic anion, binary acids (non oxyacids), polyatomic acids (oxy-acids) and hydrates.
Before we proceed any further it is extremely important for you to memorize the names,
formulas and the charges of the polyatomic anions listed on page 5 of this handout.
IUPAC nomenclature rules for inorganic compounds
1a). Binary Compounds (Metal-Nonmetal): The general formula for these compounds is
MaXb
where M = a metal or the ammonium ion (NH4+), X = a nonmetal and “a” and “b” are
small non-zero whole numbers.
These compounds may be either ionic or covalent depending on the electronegativities of
the metal and the nonmetal involved in the formation of these compounds.
The name of the metal or the ammonium ion (NH4+) is always written first. These
compounds form the general class of compounds known as salts.
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Chemistry 141
Fall 2003
Steps in naming binary metal-nonmetal compounds:
(a) Write the full name of the metal or ammonium if M is the ammonium ion.
(b) Follow the metal name with a roman numeral, in ( ), to indicate the oxidation state
of the metal. Omit this step if the metal has only one oxidation state (examples
would be alkali or alkali-earth metals or if M = NH4+).
(c) Write the stem of the nonmetal’s name. The stems for the most common
nonmetals are as follows: B = bor, C = carb, N = nitr, O = ox, F = fluor, S = silic,
P = phosph, S = sulf, Cl = chlor, I = iod, Br = brom, As = arsen, Se = selen, Te =
terllur. Write hydroxide if X = OH- or cyanide if X = CN-.
(d) Add the suffix –ide to the stem of the nonmetal’s stem.
Examples: NaCl (table salt) – Sodium chloride, MgCl2 – Magnesium chloride, FeO –
Iron (II) oxide, Fe2O3 – Iron (III) oxide.
Notice that in the above examples the names for NaCl and MgCl2 do not include the
roman numerals as these metals have only one known oxidation state. Also keep in mind
that we did not indicate the numbers of the individual metal or nonmetal ions present in
these molecules but we will do this in the next section.
1b) Binary Compounds (Nonmetal-Nonmetal): These compounds are classified as
covalent compounds or molecular compounds as they always show covalent bonding.
The least electronegative of the nonmetal is usually written first and the general formula
for these is given by:
AyBz
where A is any nonmetal, B is a different nonmetal and “y” and “z” are small non-zero
whole numbers.
Steps in naming binary nonmetal-nonmetal compounds:
Here you have to pay attention to the number of individual nonmetals present in the
formula and indicate it by adding the appropriate prefixes
(a) Write the numerical prefix for the nonmetal A (if it is one then there is no need to
write “mono”) according to the following table of prefixes:
Number Prefix
1
mono2
di3
tri
4
tetra
5
penta
6
hexa
7
hepta
8
octa
9
nona
10
deca
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Chemistry 141
Fall 2003
(b) Add the full name of the nonmetal A. If A is hydrogen then numerical prefixes
are not used.
(c) Write the numerical prefix for “z”, like with y if z = 1, then don’t write the prefix.
(d) Add the stem of the name of the second nonmetal B.
(e) Complete the name by adding the suffix –ide, to the stem of B.
Examples: CO – Carbon monoxide, CO2 – Carbon dioxide, H2S – Hydrogen sulfide,
P2O5 – Diphosphorus pentoxide.
2). Cation (metal or NH4+) – polyatomic anion: The general formula for these compounds
is given by
(Metal cation or NH4+) y (Polyatomic anion) z
The bond between the metal and the anion is always ionic and these binary compounds,
like the metal - nonmetal binary compounds, are also referred to as salts.
Steps in naming cation-polyatomic anion compounds:
(a) Name the metal ion or the ammonium ion in exactly the same manner as in the
naming of metal - nonmetal compounds.
(b) Name the polyatomic anion.
Examples: K2SO4 – Potassium sulfate, Na2CO3 – Sodium carbonate, Fe3(PO4)2 – Iron (II)
phosphate.
Notice that as long as you know the correct names for the anions and the oxidation
number of the metal, this category of compounds is the easiest to name; also we did not
use the numerical prefixes as we did before.
3). Binary acids (acids without oxygen): The general formula for these compounds is
given by
HyA (aq)
where H = hydrogen, A = an anion with a charge = y, y = a small integer and (aq) = an
aqueous (dissolved in water) solution of HyA.
Steps in naming binary acids:
(a) Write the prefix hydro - .
(b) Add the stem of the name for the nonmetal, A. If A = sulfur, write the entire
name instead of the stem.
(c) Add the suffix – ic to the stem.
(d) Add the word acid.
Examples: HCl (aq) – Hydrochloric acid; here y = 1 and it is not included in the name by
convention. It is very important to realize that a chemical will act as an acid only if
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Chemistry 141
Fall 2003
dissolved in water and will then be named as an acid. In the case of HCl if it is present as
HCl (g) it will be named as hydrogen chloride gas and not as hydrochloric acid.
H2S (aq) – Hydrosulfuric acid, even though y = 2 here the name does not include that
information.
4). Oxyacids (acids that contain polyatomic anions or oxygen): The general formula for
these acids is given by
HyXOz (aq)
where H = hydrogen, XOz y- is a polyatomic anion with a charge = y, y and z are small
integers and (aq) = dissolved in water.
Steps in naming oxyacids:
(a) Write the stem of the anion. The stem of most polyatomic anions is the name of
the anion minus the - ate or the - ite ending; for example the stem for the nitrate
ion is nitr.
(b) If the anion name originally ended in - ate add – ic to the stem of the anion.
(c) If the anion name originally ended in - ite add – ous to the stem.
(d) Add the word acid.
Examples: HNO3 (aq) – Nitric acid, HNO2 (aq) – Nitrous acid, HOCl (aq) –
Hypochlorous acid.
See the table that outlines the names for oxyacids on the last page of this handout.
5). Hydrates: The general formula is given by
Salt • y H2O
where y = a small integer.
Steps in naming hydrates:
(a) Name the salt.
(b) Give the numerical prefix for the value of y.
(c) Add the word hydrate.
Examples: CuSO4 • 5H2O – Copper (II) sulfate pentahydrate, CaSO4 • 2H2O – Calcium
sulfate dihydrate.
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Chemistry 141
Fall 2003
Polyatomic Anion Formulas and Names
You should learn all of these names, formulas and charges to be able to name
compounds that you will come across in this class. Hold on to this list if you plan on
taking any other Chemistry classes!!!
** The anions F-, Br-, I-, OF-, BrO-, BrO2-, BrO3-,
Name
Formula
BrO4-, IO-, IO2-, IO3- and IO4- are named in the
NH4+
Ammonium
exact same manner as the chlorine series.
OH Hydroxide
O2 2Peroxide
C2H3O2
Acetate
2C2O4
Oxalate
2CO3
Carbonate
HCO3
Hydrogen carbonate
(bicarbonate)
NO3
Nitrate
NO2
Nitrite
3N
Nitride
CN
Cyanide
2S
Sulfide
2SO3
Sulfite
2SO4
Sulfate
HSO4
Hydrogen sulfate
(bisulfate)
2S2O3
Thiosulfate
NCS
Thiocyanate
Cl **
Chloride
ClO
Hypochlorite
ClO2
Chlorite
ClO3
Chlorate
ClO4
Perchlorate
3PO4
Phosphate
2HPO4
Hydrogen phosphate
H2PO4
Dihydrogen phosphate
3BO3
Borate
3AsO4
Arsenate
2CrO4
Chromate
2Cr2O7
Dichromate
MnO4
Permanganate
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Chemistry 141
Fall 2003
Names for oxychloro** acids and their anions:
Acids:
Formula for
the oxyacid
HClO
Number of
Oxygen atoms
1
Prefix
used
Hypo-
Suffix
used
-ous
HClO2
HClO3
HClO4
2
3
4
--Per-
-ous
-ic
-ic
Formula for
the oxyanion
ClO-
Number of
Oxygen atoms
1
Prefix
used
Hypo-
Suffix
used
-ite
ClO2ClO3ClO4-
2
3
4
--Per-
-ite
-ate
-ate
Name of the
oxyacid
Hypochlorous
acid
Chlorous acid
Chloric acid
Perchloric acid
Anions:
Name of the
oxyanion
Hypochlorite
ion
Chlorite ion
Chlorate ion
Perchlorate ion
** Oxyacids containing the other halogens (I and Br) are named in exactly the same
manner as the oxychloro acids.
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