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Binary ionic compound
Introduction
A binary ionic compound is a salt consisting of only two elements in which both elements are ions, a cation and an anion. When naming these compounds, its composition must be considered. Type 1 binary ionic compounds are those in which the cation has only one form, or charge. Type 2 binary ionic compounds are those in which the cation can have multiple forms. Additionally, binary ionic compounds containing polyatomic ions have another distinct set of naming rules.
Naming Type I Binary Ionic compounds (metal and nonmetal):
The metals used have to be from Group 1, 2, or Al3+, Zn2+, Ag+.
1. The cation (which is a metal in most cases) is listed first and the anion (which is a nonmetal in most cases) second
2. The cation takes the name of its elemental form. For example, Li+ would be called “Lithium”.
3. The anion name uses the first part of its elemental name, and subsequently adding the suffix “-ide”. For example, Br– would be called “Bromide”
Examples: LiF (which is composed of Li+ cation and F− anion) = lithium fluoride BaO (which is composed of Ba2+ cation and O2- anion) = barium oxide
Naming Type II Binary Ionic compounds (metal and nonmetal):
Metals used are transition metals except for Al3+, Zn2+, Ag+.
1. The steps follow those of Type 1 Binary Ionic compounds however, since the cation can take on multiple charges, the charge must be written within parentheses in Roman numerals after stating the cation name.
Examples: CoO (which is composed of Co²+ cation and O²- anion) = cobalt(II) oxide FeN (which is composed of Fe³+ cation and N³- anion) = iron(III) nitride
Note that there is another way to name Type 2 ionic compounds that is not as common. This involves using an alternate, Latin name for the cation. Common Type 2 cation include Iron, Copper, Cobalt, Tin, Lead, and Mercury.
Naming Binary Compounds with Polyatomic Ions:
1. The cation is listed first and the anion second.
2. The polyatomic ion names must be memorized.
3. No extra suffixes are added.
Examples: NaCN (which is composed of Na+ cation and CN- polyatomic anion) = sodium cyanide NH4Cl (which is composed of NH4+ polyatomic cation and Cl- anion) = ammonium chloride
See also
References: Zumdahl, Steven S. Chemical Principles, Fifth Edition. New York: Houghton Mifflin, 2005. 34-39.