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 Mg magnesium ion
Al Aluminum Al 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
Fe iron(II) ion Fe iron(III) ion
Cu copper(I) ion Cu copper(II) ion

c) Cations formed from nonmetals have names ending in -ium.

Examples:

Compound Name Ion Name
NH ammonia NH ammonium ion
HO water HO 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 N nitride ion
O oxygen O oxide ion

A few simple polyatomic ions also have -ide ending.

Examples:

Polyatomic ion Name
O 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 nitrate ion NO nitrite ion
SO sulfate ion SO sulfite ion
ClO perchlorate ion ClO chlorate ion
ClO 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
CO carbonate ion HCO hydrogen carbonate ion (bicarbonate ion)
PO phosphate ion HPO 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
CaCl Ca, calcium ion Cl, chloride ion calcium chloride
Cu(ClO) Cu, copper(II) ion ClO, perchlorate ion copper(II) perchlorate
Al(SO) Al, aluminum ion SO 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
S sulfide ion HS 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
ClO perchlorate ion HClO perchloric acid
ClO chlorate ion HClO chloric acid
ClO chlorite ion HClO 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
ClO dichlorine monoxide NF nitrogen trifluoride
PF phosphorous pentafluoride ClO 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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