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
O22 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
NO3 nitrate ion NO2 nitrite ion
SO24 sulfate ion SO23 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.

Examples:

Oxyanion Name Oxyanion Name
CO23 carbonate ion HCO3 hydrogen carbonate ion (bicarbonate ion)
PO34 phosphate ion H2PO4 dihydrogen phosphate ion

3. Writing Chemical Names from Formulas

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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

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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:

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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:

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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 ClO4, perchlorate ion copper(II) perchlorate
Al2(SO4)3 Al3+, aluminum ion SO4 sulfate ion aluminum sulfate

5. Acids

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

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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.

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Examples:

Oxyanion Name Oxyacid Name
ClO4 perchlorate ion HClO4 perchloric acid
ClO3 chlorate ion HClO3 chloric acid
ClO2 chlorite ion HClO2 chlorous acid
ClO hypochlorite ion HClO hypochlorous acid

6. Binary Molecular Compounds

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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.)

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Examples:

Compound Name Compound Name
Cl2O dichlorine monoxide NF3 nitrogen trifluoride
PF5 phosphorous pentafluoride Cl2O4 dinitrogen tetroxide

Click here to try out the Part A quiz for this section.

When you're confident in the skill, take the Part B quiz!

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