HOW TO NAME INORGANIC COMPOUNDS AND IONS

1. Positive ions (cations)

a) Cations formed from metal atoms have the same name as the metal

K⁺  potassium ion,   Mg²⁺ magnesium ion, Al³⁺ aluminum ion

b) If metal forms cations of differing charges, the positive charge is given by a roman numeral in parenthesis

Fe²⁺  iron(II) ion,  Fe³⁺ iron(III) ion,  Cu⁺ copper(I) ion, Sn²⁺ tin(II) ion 

c) cations formed from nonmetals have names ending in -ium

NH₄⁺ ammonium ion, H₃O⁺ hydronium ion

2. Negative ions (anions)

a) Monoatomic anions are formed by replacing the ending of the name of the element with -ide. A few simple polyatomic ions also have -ide ending. 

H^- hydride ion,  O^2-  oxide ion, N^3- nitride ion
HO^- hydroxide ion, CN^- cyanide ion, O₂^2- peroxide ion

b) Oxyanions (polyatomic ions containing oxygen) have endings -ate (used for the most common ion of an element) or -ite. (used for the ion with the same charge but one less oxygen atom).  Prefixes (per- and hypo-) are used for oxyanions with more members in the series.

NO₃^- nitrate ion, NO₂^- nitrite ion, SO₄^2- sulfate ion, SO₃^2- sulfite ion
ClO₄^- perchlorate ion, ClO₃^- chlorate ion, ClO₂^- chlorite ion, ClO^- hypochlorite ion

c) anions derived by adding H⁺ to an oxyanion are named by adding hydrogen- (or dihydrogen- etc.) as a prefix. 

HCO₃^- hydrogen carbonate ion, H₂PO₄^- dihydrogen phosphate ion

3. Ionic compounds

The names of ionic compounds are composed of the cation name followed by the anion name. 

NaCl sodium chloride, Al(NO₃)₃ aluminum nitrate, Cu(ClO₄)₂ copper(II) perchlorate

4. Acids

a) Acids based on anions ending with -ide have hydro- prefix and -ic ending.  

Cl^- chloride:  HCl hydrochloric acid, S^2- sulfide: H₂S hydrosulfuric acid

b) If the name of the anions ends in -ate the acid have -ic ending, and if the name of the anions ends in -ite the acid have -ous ending

ClO₄^- perchlorate: HClO₄ perchloric acid, ClO₂^- chlorite: HClO₂ chlorous acid

5. Binary Compounds

Compounds containing two elements  are named by listing both elements, usually starting with the element farthest to the left in the periodic table. The second element is given -ide ending. Greek prefixes are used to indicate the number of atoms.

Cl₂O dichlorine monoxide, NF₃ nitrogen trifluoride, N₂O₄ dinitrogen tetroxide 

In the table below you can find the names of ions and compounds that you should know (they will be used on quizzes and exams).

(acids in parenthesis are very weak acids)

    Tutorials  

 Last updated 01/12/07

 Copyright 2000-2006