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⁺ + 2N^3- --> 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 (CO₃^2-)
zinc (Zn²⁺)	chromate (CrO₄^2-)
	dichromate (Cr₂O₇^2-)
3+	hydrogen phosphate (HPO₄^2-)
aluminum (Al³⁺)	oxide (O^2-)
chromium(III) (Cr³⁺)	peroxide (O₂^2-)
iron(III) (Fe³⁺)	sulfate (SO₄^2-)
	sulfide (S^2-)
	sulfite (SO₃^2-)
	3-
	nitride (N^3-)
	phosphate (PO₄^3-)
	phosphide (P^3-)

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:
- O^2- = 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

ClO₂^- = chlorite
NO₂^- = nitrite
SO₃^2- = sulfite

Most common oxyanions with four oxygens

SO₄^2- = sulfate
PO₄^3- = phosphate
CrO₄^2- = chromate

Most common oxyanions with three oxygens

NO₃^- = nitrate
ClO₃^- = chlorate
CO₃^2- = 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 beginning

Example:
CO₃^2- 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^- --> NaCl
  sodium + chloride --> sodium chloride
- Cu²⁺ + SO₄^2- -->CuSO₄
  copper(II) + sulfate --> copper(II) sulfate
- Al³⁺ + 3NO₃^- --> Al(NO₃)₃
  aluminum + 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 dioxide
P₄S₁₀ = 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 acid
HBr = 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 acid
ClO^- 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 C_nH_2n+2
Double bonds (alkene): suffix is "ene", formula C_nH_2n
Triple bonds (alkyne): suffix is "yne", formula C_nH_2n-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 tetraoxide
S₂F₁₀ = 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

A solution set is available for viewing.

[Basic Index] [Chemical Nomenclature] [Atomic Structure] [Periodic Table]
[Lewis Structure] [Chemical Reactions] [Stoichiometry] [Acid-Base Chemistry]

Developed by

Shodor
in cooperation with the Department of Chemistry,
The University of North Carolina at Chapel Hill