Rules for naming inorganic ionic and covalent types of chemical compounds
See also Naming of Organic Compounds
Binary ionic compounds contain a positiv ion (cation) and a negative ion (anion). The cation is a metal in most cases, and is always written first in the formula. The anion is a nonmetal in most cases.
In the naming, these rules must be followed:
- The cation is always named first and the anion second.
- A cation takes its name from the name of the element. Example: K+ is called potassium in the names of compounds containing this ion.
- An anion is named by taking the first part of the element name and adding -ide. Example: the Br- ion is called bromide.
A monatomic ion is an ion consisting of a single atom. Examples are given in the table:
|Monatomic cations and anions|
A polyatomic ion contains more than one atom, these atoms can be of the same element or of different elements.
There are polyatomic anion series with one given element together with different numbers of oxygen atoms, called oxyanions:
- In oxyanion series with two members, the name of the one with the smaller number of oxygen atoms ends in -ite.
- The name of the one with the larger number ends in -ate.
- When more than two oxyanions make up a series,
- hypo- (less than) are used as prefix to name the member of the series with the fewest oxygen atoms.
- per- (more than) are used as prefix to name the member of the series with the most oxygen atoms.
|HCO3-||Hydrogen carbonate (or bicarbonate)||OH-||Hydroxide|
|Cr2O7-||Dichromate||HSO4-||Hydrogen sulfate (or bisulfate)|
Type I binary ionic compounds contains a metal that forms only one type of cation. Examples: Na+ and Ca2+ . Examples of naming of compounds type I is given in the table:
|Type I compounds, naming examples|
|CaS||Ca2+, S2-||Calcium sulfide|
|CsBr||Cs+, Br-||Cesium bromide|
|Li3N||Li+, N3-||Lithium nitride|
|MgO||Mg2+, O2-||Magnesium oxide|
|KF||K+, F-||Potassium fluoride|
|AgI||Ag+, I-||Silver iodide|
|NaCl||Na+, Cl-||Sodium chloride|
Type II binary ionic compounds can form more than one type of cation. Examples: Fe2+ and Fe3+, Pb2+ and Pb4+.
For type II compounds the charge of the metal ion must be specified, and this is systematically done with Roman numeral indication.
Example: iron(II) for Fe2+ and iron(III) for Fe3+. Then, the compounds with formula FeCl2 and FeCl3 are called iron(II) chloride and iron(III) chloride, respectively.
An older way to separate between metal ions that forms two different charges:
The ion with the lower charge has a name ending in -ous and the one with the higher charge has a name ending in -ic.
|Type II cations|
|Ion||Systematic name||Alternate name|
Covalent compounds (contain two nonmetals)
Rules for naming binary covalent compounds:
Nonmetal X + Nonmetal Y + "-ide"
- The first element in the formula is named first, using the full element name
- The second element is named as if it were an anion.
- Prefixes are used to denote the numbers of atoms present (mono-, di-, tri-, tetra-, penta-, hexa-, hepta-, octa-)
- The prefix mono- is never used for naming the first element. Example: CO is called carbon monoxide (not monocarbon monoxide).
- Some elements beginning with vowels (Oxygen, for example) replace the vowel ending -o or -a of its prefix; mono- + Oxide = Monoxide, O4 = Tetroxide, O5 = Pentoxide, and so on.
|Examples of naming covalent compounds with nitrogen and oxygen|
|Compound||Systematic name||Common name|
|NO||Nitrogen monoxide||Nitric oxide|
|N2O||Dinitrogen monoxide||Nitrous oxide|