Chemical Nomenclature
Chemical nomenclature is the term given to the naming of compounds. Chemists use specific rules and "conventions" to name different compounds. This section is designed to help you review some of those rules and conventions.
Oxidation and Reduction
Forming Ionic Compounds
Arrangement of Atoms
Naming Ionic Compounds
Naming Binary Molecular Compounds
Naming Inorganic Acids
Naming Compounds
Oxidation and Reduction
When forming compounds, it is important to know something about the way atoms will react with each other. One of the most important manners in which atoms and/or molecules react with each other is the oxidation/reduction reaction. Oxidation/Reduction reactions are the processes of losing and gaining electrons respectively. Just remember, "LEO the lion says GER:" Lose Electrons Oxidation, Gain Electrons Reduction. Oxidation numbers are assigned to atoms and compounds as a way to tell scientists where the electrons are in a reaction. It is often referred to as the "charge" on the atom or compound. The oxidation number is assigned according to a standard set of rules. They are as follows:
An atom of a pure element has an oxidation number of zero.
For single atoms in an ion, their oxidation number is equal to their charge.
Fluorine is always -1 in compounds.
Cl, Br, and I are always -1 in compounds except when they are combined with O or F.
H is normally +1 and O is normally -2.
The oxidation number of a compound is equal to the sum of the oxidation numbers for each atom in the compound.
Forming Ionic Compounds
Knowing the oxidation number of a compound is very important when discussing ionic compounds. Ionic compounds are combinations of positive and negative ions. They are generally formed when nonmetals and metals bond. To determine which substance is formed, we must use the charges of the ions involved. To make a neutral molecule, the positive charge of the cation (positively-charged ion) must equal the negative charge of the anion (negatively-charged ion). In order to create a neutral charged molecule, you must combine the atoms in certain proportions. Scientists use subscripts to identify how many of each atom makes up the molecule. For example, when combining magnesium and nitrogen we know that the magnesium ion has a "+2" charge and the nitrogen ion has a "-3" charge. To cancel these charges, we must have three magnesium atoms for every two nitrogen atoms:
3Mg2+ + 2N3- --> Mg3N2
Knowledge of the charges of ions is crucial to knowing the formulas of the compounds formed.
alkalis (1st column elements) form "+1" ions such as Na+ and Li+
alkaline earth metals (2nd column elements) form "2+" ions such as Mg2+ and Ba2+
halogens (7th column elements) form "-1" ions such as Cl- and I-
Other common ions are listed in the table below:
Positive ions (cations)
Negative ions (anions)
1+
1-
ammonium (NH4+)
acetate (C2H3O2-)
copper(I) (Cu+)
azide (N3-)
hydrogen (H+)
chlorate (ClO3-)
silver (Ag+)
cyanide (CN-)

dihydrogen phosphate (H2PO4-)
2+
hydride (H-)
cadmium (Cd2+)
bicarbonate (HCO3-)
cobalt(II) (Co2+)
hydroxide (OH-)
copper(II) (Cu2+)
nitrate (NO3-)
iron (Fe2+)
nitrite (NO2-)
lead (Pb2+)
perchlorate (ClO4-)
manganese(II) (Mn2+)
permanganate (MnO4-)
mercury(I) (Hg22+)
thiocyanate(SCN-)
mercury(II) (Hg2+)

nickel (Ni2+)
2-
tin (Sn2+)
carbonate (CO32-)
zinc (Zn2+)
chromate (CrO42-)

dichromate (Cr2O72-)
3+
hydrogen phosphate (HPO42-)
aluminum (Al3+)
oxide (O2-)
chromium(III) (Cr3+)
peroxide (O22-)
iron(III) (Fe3+)
sulfate (SO42-)

sulfide (S2-)

sulfite (SO32-)

3-

nitride (N3-)

phosphate (PO43-)

phosphide (P3-)
Naming Ionic Compounds
The outline below provides the rules for naming ionic compounds:
Positive Ions
Monatomic cations (a single atom with a positive charge) take the name of the element plus the word "ion"Examples:
Na+ = sodium ion
Zn+2 = zinc ion

If an element can form more than one (1) positive ion, the charge is indicated by the Roman numeral in parentheses followed by the word "ion"Examples:
Fe2+ = iron(II) ion
Fe3+ = iron (III) ion
Negative Ions
Monatomic anions (a single atom with a negative charge) change their ending to "-ide"Examples:
O2- = oxide ion
Cl- = chloride ion

Oxoanions (negatively charged polyatomic ions which contain O) end in "-ate". However, if there is more than one oxyanion for a specific element then the endings are:
Two less oxygen than the most common starts with "hypo-" and ends with "-ite"
One less oxygen than the most common ends with "-ite"
THE MOST COMMON OXOANION ENDS WITH "-ATE"
One more oxygen than the most common starts with "per-" and ends with "-ate"
ClO- = hypochlorite
o ClO2- = chlorite
o NO2- = nitrite
o SO32- = sulfite
Most common oxyanions with four oxygens
o SO42- = sulfate
o PO43- = phosphate
o CrO42- = chromate
Most common oxyanions with three oxygens
o NO3- = nitrate
o ClO3- = chlorate
o CO32- = carbonate
ClO4- = perchlorate

Polyatomic anions (a negatively charged ion containing more than one type of element) often add a hydrogen atom; in this case, the anion's name either adds "hydrogen-" or "bi-" to the beginningExample:CO32- becomes HCO3-"Carbonate" becomes either "Hydrogen Carbonate" or "Bicarbonate"
When combining cations and anions into an ionic compound, you always put the cation name first and then the anion name (the molecular formulas are also written in this order as well.)Examples:
Na+ + Cl- --> NaClsodium + chloride --> sodium chloride
Cu2+ + SO42- -->CuSO4copper(II) + sulfate --> copper(II) sulfate
Al3+ + 3NO3- --> Al(NO3)3aluminum + nitrate --> aluminum nitrate
Arrangement of Atoms
In naming ions, it is important to consider "isomers." Isomers are compounds with the same molecular formula, but different arrangements of atoms. Thus, it is important to include some signal within the name of the ion that identifies which arrangement you are talking about. There are three main types of classification, geometric, optical and structural isomers.
Geometric isomers refers to which side of the ion atoms lie. The prefixes used to distinguish geometric isomers are cis meaning substituents lie on the same side of the ion and trans meaning they lie on opposite sides. Below is a diagram to help you remember.
Optical isomers differ in the arrangement of four groups around a chiral carbon. These two isomers are differentiated as L and D.
Structural isomers differentiate between the placement of two chlorine atoms around a hexagonal carbon ring. These three isomers are identified as o, m, and p. Once again we have given you a few clues to help your memory.
A pop-up nomenclature calculator is available for help when naming compounds and for practice problems.
Naming Binary Molecular Compounds
Molecular compounds are formed from the covalent bonding between non-metallic elements. The nomenclature for these compounds is described in the following set of rules.
The more positive atom is written first (the atom which is the furthest to the left and to the bottom of the periodic table)
The more negative second atom has an "-ide" ending.
Each prefix indicates the number of each atom present in the compound.
Number of Atoms
Prefix
Number of Atoms
Prefix
1
mono
6
hexa
2
di
7
hepta
3
tri
8
octa
4
tetra
9
nona
5
penta
10
deca
Examples:CO2 = carbon dioxideP4S10 = tetraphosphorus decasulfide
Naming Inorganic Acids
Binary acids (H plus a nonmetal element) are acids that dissociate into hydrogen atoms and anions in water. Acids that only release one hydrogen atom are known as monoprotic. Those acids that release more than one hydrogen atom are called polyproticacids. When naming these binary acids, you merely add "hydro-" (denoting the presence of a hydrogen atom) to the beginning and "-ic acid" to the end of the anion name.Examples:HCl = hydrochloric acidHBr = hydrobromic acid
Ternary acids (also called oxoacids, are formed by hydrogen plus another element plus oxygen) are based on the name of the anion. In this case, the -ate, and -ite suffixes for the anion are replaced with -ic and -ous respectively. The new anion name is then followed by the word "acid." The chart below depicts the changes in nomenclature.
Anion name
Acid name
hypo___ite
hypo___ous acid
___ite
___ous acid
___ate
___ic acid
per___ate
per___ic acid
Example:ClO4- to HClO4 => perchlorate to perchloric acidClO- to HClO => hypochlorite to hypochlorous acid
Naming Compounds
A detailed treatise on naming organic compounds is beyond the scope of these materials, but some basics are presented. The wise chemistry student should consider memorizing the prefixes of the first ten organic compounds:
Number of Carbons
Prefix
1
meth-
2
eth-
3
prop-
4
but-
5
pent-
6
hex-
7
hept-
8
oct-
9
non-
10
dec-
There are four basic types of organic hydrocarbons, those chemicals with only carbon and hydrogen:
Single bonds (alkane): suffix is "ane", formula CnH2n+2
Double bonds (alkene): suffix is "ene", formula CnH2n
Triple bonds (alkyne): suffix is "yne", formula CnH2n-2
Cyclic compounds: use prefix "cyclo"
So, for example, an organic compound with the formula "C6H14" would be recognized as an alkane with six carbons, so its name is "hexane".
Examples:N2O4 = dinitrogen tetraoxideS2F10 = disulfur decafluoride
Practice Problems
Find the formulas of the following molecules:
1.
aluminum fluoride


8.
ammonium dichromate
2.
carbon tetrachloride


9.
magnesium acetate
3.
strontium nitrate


10.
zinc hydroxide
4.
sodium bisulfate


11.
nitric acid
5.
iron(III) oxide


12.
hypochlorous acid
6.
mercury(II) nitrate


13.
phosphoric acid
7.
sodium sulfite


14.
aluminum nitrate
A solution set is available for viewing.
Write the names of the following molecules:
1.
CaCO3


8.
Mg3(PO4)2
2.
SCl2


9.
Ba(NO2)2
3.
Li2CrO4


10.
Hg2Cl2
4.
NaSCN


11.
NaHCO3
5.
KClO3


12.
H2S
6.
Ca(C2H3O2)2


13.
H2SO3
7.
K2Cr2O7


14.
SO3