Naming Ions and Ionic Compounds
Ionic compounds consist of cations (positive ions) and anions (negative ions).
The nomenclature, or naming, of ionic compounds is based on the names of the component ions.
Here are the principal naming conventions for ionic compounds, along with examples to show how they are used:
A Roman numeral in parentheses, followed by the name of the element, is used for elements that can form more than one positive ion.
This is usually seen with metals.
Fe 2+ Iron (II)
Fe 3+ Iron (III)
Cu + Copper (I)
Cu 2+ Copper (II)
-ous and -ic
Although Roman numerals are used to denote the ionic charge of cations, it is still common to see and use the endings -ous or -ic. These endings are added to the Latin name of the element (e.g., stannous/stannic for tin) to represent the ions with lesser or greater charge, respectively.
The Roman numeral naming convention has wider appeal because many ions have more than two valences.
Fe 2+ Ferrous
Fe 3+ Ferric
Cu + Cuprous
Cu 2+ Cupric
The -ide ending is added to the name of a monoatomic anion of an element.
H - Hydride
F - Fluoride
O 2- Oxide
S 2- Sulphide
N 3- Nitride
P 3- Phosphide
-ite and -ate
Some polyatomic anions contain oxygen. These anions are called oxyanions. When an element forms two oxyanions, the one with less oxygen is given a name ending in -ite and the one with more oxygen is given a name that ends in -ate.
NO2 - Nitrite
NO3 - Nitrate
SO3 2- Sulphite
SO4 2- Sulphate
hypo- and per-
In the case where there is a series of four oxyanions, the hypo- and per- prefixes are used in conjunction with the -ite and -ate suffixes. The hypo- and per- prefixes indicate less oxygen and more oxygen, respectively.
ClO - Hypochlorite
ClO2 - Chlorite
ClO3 - Chlorate
ClO4 - Perchlorate
bi- and di- hydrogen
Polyatomic anions sometimes gain one or more H+ ions to form anions of a lower charge. These ions are named by adding the word hydrogen or dihydrogen in front of the name of the anion. It is still common to see and use the older naming convention in which the prefix bi- is used to indicate the addition of a single hydrogen ion.
HCO3 - Hydrogen carbonate or bicarbonate
HSO4 - Hydrogen sulfate or bisulfate
H2PO4 - Dihydrogen phosphate
Naming Binary Acids
Binary acids are compounds containing Hydrogen and an anion (non-metal ion).
When these compounds are in solution in water, oxonium ions (H3O+) are formed giving rise to the properties that we associate with 'acids'.
In general, when the binary acid is not in solution the name is as follows: 'Hydrogen' followed by the anion name ending in '-ide'.
e.g. Hydrogen chloride
When the binary acid is in solution (aq) the name is as follows: 'Hydro-' followed by the anion name ending in '-ic' then add the word 'acid' to the end.
e.g. Hydrochloric acid