Naming Chemical Compounds
The rules for naming ions, ionic compounds, and inorganic molecular compounds are summarized below:
1. Positive ions (cations)
a) Cations formed from metal atoms have the same name as the metal. This is common for metals in groups 1 and 2 on the periodic table (as well as aluminum, zinc, and silver).
Examples:
Metal | Name | Metal Ion | Name |
---|---|---|---|
K | potassium | K+ | potassium ion |
Mg | magnesium | Mg2+ | magnesium ion |
Al | Aluminum | Al3+ | aluminum ion |
b) For metals that form cations of differing charges, the positive charge is given by a roman numeral in parentheses. This will be the case for transition metals and a few metals in the main group (i.e. lead and tin).
Examples:
Metal Ion | Name | Metal Ion | Name |
---|---|---|---|
Fe2+ | iron(II) ion | Fe3+ | iron(III) ion |
Cu+ | copper(I) ion | Cu2+ | copper(II) ion |
c) Cations formed from nonmetals have names ending in -ium.
Examples:
Compound | Name | Ion | Name |
---|---|---|---|
NH3 | ammonia | NH+4 | ammonium ion |
H2O | water | H3O+ | hydronium ion |
2. Negative ions (anions)
a) Monoatomic anions are formed by replacing the ending of the name of the element with -ide.
Examples:
Nonmetal | Name | Ion | Name |
---|---|---|---|
H | hydrogen | H− | hydride ion |
N | nitrogen | N3− | nitride ion |
O | oxygen | O2− | oxide ion |
A few simple polyatomic ions also have -ide ending.
Examples:
Polyatomic ion | Name |
---|---|
O2−2 | peroxide ion |
CN− | cyanide ion |
OH− | hydroxide 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.
Examples:
Oxyanion | Name | Oxyanion | Name |
---|---|---|---|
NO−3 | nitrate ion | NO−2 | nitrite ion |
SO2−4 | sulfate ion | SO2−3 | sulfite ion |
ClO−4 | perchlorate ion | ClO−3 | chlorate ion |
ClO−2 | 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.
Examples:
Oxyanion | Name | Oxyanion | Name |
---|---|---|---|
CO2−3 | carbonate ion | HCO−3 | hydrogen carbonate ion (bicarbonate ion) |
PO3−4 | phosphate ion | H2PO−4 | dihydrogen phosphate ion |
3. Writing Chemical Names from Formulas
[ciscode|rev=1|tool=elmsmedia|item=3211|entity_type=node|render=display_mode|display_mode=mediavideothumbnailright]
Now that we can identify metal ions, let's first look at how we can write a name from a given chemical formula. Check out the video on the right.
4. Ionic compounds
[ciscode|rev=1|tool=elmsmedia|item=3212|entity_type=node|render=display_mode|display_mode=mediavideothumbnailright]
Metals in groups 1, 2, and 3 on the periodic table form only one type of ion. The names of of ionic compounds containing one of these metals will take the following form:
Transition metals and a handful of main group metals have several possible charge states. The names of of ionic compounds containing a metal with multiple oxidation states take the following form:
Examples:
Compound | Cation & Name | Anion & Name | Compound Name |
---|---|---|---|
NaCl | Na+, sodium ion | Cl−, chloride ion | sodium chloride |
CaCl2 | Ca2+, calcium ion | Cl−, chloride ion | calcium chloride |
Cu(ClO4) | Cu2+, copper(II) ion | ClO−4, perchlorate ion | copper(II) perchlorate |
Al2(SO4)3 | Al3+, aluminum ion | SO−4 sulfate ion | aluminum sulfate |
5. Acids
[ciscode|rev=1|tool=elmsmedia|item=3213|entity_type=node|render=display_mode|display_mode=mediavideothumbnailright]
a) Acids based on anions ending with -ide have hydro- prefix and -ic ending.
Examples:
Anion | Name | Oxyanion | Name |
---|---|---|---|
Cl− | chloride ion | HCl | hydrochloric acid |
S2− | sulfide ion | H2S | hydrosulfuric acid |
b) If the name of an anion ends in -ate, the acid will end in -ic. If the name of an anion ends in -ite, the acid will end in -ous.
Examples:
Oxyanion | Name | Oxyacid | Name |
---|---|---|---|
ClO−4 | perchlorate ion | HClO4 | perchloric acid |
ClO−3 | chlorate ion | HClO3 | chloric acid |
ClO−2 | chlorite ion | HClO2 | chlorous acid |
ClO− | hypochlorite ion | HClO | hypochlorous acid |
6. Binary Molecular Compounds
[ciscode|rev=1|tool=elmsmedia|item=3214|entity_type=node|render=display_mode|display_mode=mediavideothumbnailright]
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 the -ide ending. Greek prefixes are used to indicate the number of atoms. (Note: The "mono-" prefix is typically omitted from the beginning of the name.)
Examples:
Compound | Name | Compound | Name |
---|---|---|---|
Cl2O | dichlorine monoxide | NF3 | nitrogen trifluoride |
PF5 | phosphorous pentafluoride | Cl2O4 | dinitrogen tetroxide |