Chemical compounds as classified as organic or inorganic.    Organic compounds are compounds that contain carbon usually in combination with elements such as hydrogen, nitrogen and oxygen.   Inorganic compounds are compounds composed of elements other than carbon.   A few simple compounds of carbon such as carbon monoxide, carbon dioxide, carbonates and cyanides are considered to be inorganic compounds.

Binary Ionic Compounds

A binary ionic compound is a compound composed of ions from only two elements.  Usually these compounds consist of a metal, which is the positive ion (cation), and a nonmetal, which is the negative ion (anion).  Some examples of binary ionic compounds are MgO, Na₂O, and CaCl₂

Naming Binary Ionic Compounds When the Metal Forms only one Cation

The metals in group IA, IIA as well as zinc, cadmium, aluminum, gallium, and indium form only a single cation.   The following rules are used to name this type of ionic compound.

1.   The name of the cation is taken from the name of the metallic element without modification.

2.   The name of the anion is derived from the element's name by retaining the root and adding the suffix -ide.

3.   The name of the binary ionic compound is always two words.    The name of the cation is given first (omitting the word ion) followed by the name of the anion again omitting the word ion.

Some examples would be NaCl, sodium chloride, CdO, cadmium oxide, and Mg₃P₂, magnesium phosphide.

Naming Binary Ionic Compounds When the Metal Forms More Than one Cation

Cations formed from tin, lead, the transition metals (B group elements) and a few other elements can have two or more charges.   For example iron can form two compounds with oxygen: FeO and Fe₂O₃. If we were to name these two compounds according to the rules in the preceding section, each would be named iron oxide.    Clearly,  we must have a different way of naming compounds containing cations with more than one possible charge.

The Stock Method

In the Stock method of naming ionic compounds, the magnitude of the positive charge on the cation is designated by a Roman numeral in parentheses immediately following the name of the metallic element. (Do not leave a space between the name of the metallic element and the first parenthesis - Chemists are very "picky" about this.)   The  Stock method does not change the name of the nonmetal in any way.    Applying this method to the two compounds of iron above we would arrive at the name iron(II) oxide for FeO (the cation in this compound is Fe²⁺) and for Fe₂O₃, iron(III) oxide (the cation here is Fe³⁺).

Remember it is incorrect to use the Stock system when only one binary ionic compound can be formed from a pair of elements.   You would not use the name sodium(I) chloride, since a sodium ion can have only one charge.

The Classical Method

An older method of naming ionic compounds now being phased out is called the classical method.   In this method, the names of the two most common ions derived from a metallic element share a common root but are distinguised by the suffix -ous for the one with the lower charge and -ic for the one with the higher charge.   Latin roots are used if the symbol for the element is derived from a Latin word.    To use our iron compounds again, the name of FeO would be ferrous oxide and Fe₂O₃, would be ferric oxide.

Names of Selected Ions by the Two Methods

Naming Compounds Containing Polyatomic Ions

A polyatomic ion contains a group of chemically bonded atoms act as a single unit.  This group of atoms carries an electrical charge that is associated with the group of atoms not any one atom in the group.  Most polyatomic ions are anions, one notable exception in the ammonium ion, NH₃⁺.   A subcategory of the polyatomic ions is a group of anions called oxyanions.  These are anions that have one or more atoms of oxygen in addition to another atom.  Included in the comon polyatomic ions are several series of oxyanions that differ only in the number on oxygen atoms they contain.   If there are only two oxyanions in the series, the name of the one with the fewer oxygen atoms will end in -ite and the one with the higher number will end with -ate.   If more than two oxyanions are in a series, the names will also include the prefix per- for the one with the most oxygen and the prefix hypo- for the oxyanion with the fewest oxygen atoms.  When the prefix per- is used the suffix is always -ate, and when the prefix is hypo-, the suffix is always -ite.   The table below lists some common polyatomic ions.  Since there are very few rules associated with the names of polyatomic ions, the names must be memorized.   The name of a polyatomic ionic compound will consist of two words as in the case of the binary compounds.   The first word in the name is that of the cation using the same rules as with the binary compounds followed by the name of the polyatomic anion from the table below.