- Nomenclature -
Naming Chemical Compounds
An Internet Review Lesson


Table of Contents

General Information
Ionic Formulas
   Binary
   Polyatomic
   Multiple Valence Numbers
Binary Molecular Formulas
Acids
Practice
Naming Quiz



 

General Information

Scientist all around the globe use a standard method for naming chemical compounds.  The standards were set up by an international committee sponsored by the IUPAC.  Having this standard makes life easier for people who use these compounds everyday.  It would be tough to set up any experiment if scientists everywhere used different names for the same compound. It would also make the lab a much more dangerous place.  Although there are other types of compounds, for this lesson we will concentrate on ionic formulas, both binary and polyatomic, binary molecular formulas, and the formulas for acids.

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Ionic Formulas

Ionic formulas are constructed of particles with opposite charges. The positive particles are referred to as the cations, the negatively charged particles are the anions. For this section, three types of ionic formulas will be discussed.

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Binary Ionic Formulas - Binary formulas contain two elements. For binary ionic formulas, the first element in the formula will be the cation and second element will be the anion. An easy way to recognize this type of formulas, is that the first element will be a metal and the second element will be a nonmetal.  So, in general, the first element in the compound will come from the left side of the periodic table and the second element will be from the right side.  To name a binary ionic compound you will consider the cation and anion separately.  The name of the cation is the regular name of the element.
The ending of the anion is changed to -ide.

Examples:

NaCl
- sodium chloride 
MgO
- magnesium oxide
CaBr2
 - calcium bromide
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Polyatomic Formulas - Polyatomic ions are made from more that one atom.  This group of atoms act together as one unit with a single charge. Each of the polyatomic ions have a unique name.

Table of Polyatomic Ions

1+
1-
2-
3-
ammonium , NH4 + acetate, C2H302- carbonate, CO32- phosphate, PO43-
bicarbonate, HCO3 - chromate,CrO42-
bisulfate, HSO4 - dichromate,Cr2O72-
bisulfite, HSO3 - oxalate,C2O42-
chlorate,ClO3- peroxide,022-
chlorite,ClO2- silicate,SiO32-
cyanide,CN- sulfate,SO42-
hydroxide,OH- sulfite,SO32-
hypochlorite,ClO- tartrate,C4H4062-
iodate,IO3- thiosulfate,S2O32-
nitrate,NO3-
nitrite,NO2-
perchlorate,ClO4-
permanganate,MnO4-

Most of the polyatomic ions are anions.  The formula for the compound will contain both a cation and an anion to balance the overall charge of the compound. The cation is named normally and the anion is given the name of the actual anion.  An easy way to recognize these formulas is the fact that they are made up of more that two elements and, usually, the first element is a metal.

Examples:

Al(C2H3O2)3
- aluminum acetate
KCN
- potassium cyanide
BaSO3
- barium sulfate
CaSO3
- calcium sulfite
Li3PO4
- lithium phosphate
NH4OH
 - ammonium hydroxide
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Multiple Ionic Charges - The ionic charges of several transition metals are variable.  For example the copper ion can either be 1+ or 2+.

Table of Metal Ions with Multiple Valence Numbers
 

 antimony (III)
- Sb3+
iron (II)
- Fe2+
mercury (I) 
- Hg2+2
antimony (IV)
- Sb5+
iron (III)
- Fe3+
mercury (II)
- Hg2+
chromium (II)
- Cr2+
lead (II)
- Pb2+
nickel (II)
- Ni2+
chromium (III)
- Cr3+
lead (IV)
- Pb4+
nickel (III)
- Ni3+
copper (I)
- Cu +
manganese (II)
- Mn2+
tin (II)
- Sn2+
copper (II)
- Cu2+
manganese (IV)
- Mn4+
tin (IV)
- Sn4+
The name of the compound should have a roman numeral placed between the name of the cation and the anion to indicate the specific charge of the cation being used.  To determine this charge you need to determine what charge is needed to balance the overall compound.  To do this multiply the charge of the anion by the number of anions divide this by the number of cations.  This will give the charge for the cation.

Examples:

FeO
- iron II oxide
PbO
- lead II oxide
Fe2O3
- iron III oxide
PbO2
- lead IV oxide
CuOH
- copper I hydroxide
Cr(NO3)2
- chromium II nitrite
Cu(OH)2
- copper II hydroxide
Cr(NO3)3
- chromium III nitrite
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Binary Molecular Formulas - Molecules are compounds that use covalent bonds to join two atoms together.  Binary molecules will only have two elements in their formula.  An easy way to determine if the compound is named in this manner, is the fact that the two elements in the formula will both be nonmetals (or both are from the right hand side of the periodic table).  The names of the compounds will include a prefix to indicate the number of atoms of each element.  There is no need to balance this type of formula.  The second elements name is changed to end in -ide.

Table of Prefixes

one -
mono
six - 
hexa
two - 
di
seven - 
hepta
three - 
tri
eight - 
octa
four - 
tetra
nine - 
nona
five - 
penta
ten - 
deca
An exception to using the prefixes is when the first element has only one atom. The prefix would be mono is not used for this instance.  Also determining where the words fit together will take some practice.

Examples:

CO2
 - carbon dioxide
CCl4
 - carbon tetrachloride
S3N2
 - trisulfur dinitride
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Acids - Acids dissociate into ions when disolved in water.  All of the formulas for acids that are dealt with in this section will start with the hydrogen ion.  In order to name the compound as an acid, first name the compound as if it were an ionic compound. Use hydrogen as the cation. Then change the name according to the following table.

Table for Naming Acids
 

Ending of name as an ionic compound
New form of name
-ide
hydro-root-ic acid
-ite
root-ous acid
-ate
root-ic acid
Examples:
Formula
Ionic Name
Acidic Name
HCl
hydrogen chloride
hydrochloric acid
HNO3
hydrogen nitrate
nitric acid
H2SO3
hydrogen sulfite
sulfurous acid
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Practice Click here for practice naming compounds.
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