Names and Formulas of
Ternary Ionic Compounds
Ck12 Science
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Printed: November 19, 2015
AUTHOR
Ck12 Science
www.ck12.org
C HAPTER
Chapter 1. Names and Formulas of Ternary Ionic Compounds
1
Names and Formulas of
Ternary Ionic Compounds
• Be able to write structures for ternary ionic compounds when given the name.
• Be able to name ternary ionic compounds when given the structures.
Most people enjoy eating pizza. When they order a pizza (either by phone, on-line, or in a restaurant), they don’t just
order “pizza.” Even the simplest “binary” pizza will have a topping and cheese –maybe pepperoni, maybe something
else. However, many pizzas quickly become more complex. One person may want pepperoni and sausage, another
may wish to order Canadian bacon and pineapple, and then you have the folks that can’t decide, so they order
half-this and half-that. The combinations may be more complex, but the same basic ideas about pizza are valid.
Ternary Ionic Compounds
Not all ionic compounds are composed of only monatomic ions. A ternary ionic compound is an ionic compound
composed of three or more elements. In a typical ternary ionic compound, there is still one type of cation and one
type of anion involved. The cation, the anion, or both, is a polyatomic ion.
Naming Ternary Ionic Compounds
The process of naming ternary ionic compounds is the same as naming binary ionic compounds. The cation is named
first, followed by the anion. Some examples are shown in the Table 1.1:
TABLE 1.1: Examples of Ternary Ionic Compounds
Formula
Name
1
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TABLE 1.1: (continued)
NaNO3
NH4 Cl
Fe(OH)3
sodium nitrate
ammonium chloride
iron(III) hydroxide
When more than one polyatomic ion is present in a compound, the formula of the ion is placed in parentheses with a
subscript outside of the parentheses that indicates how many of those ions are in the compound. In the last example
above, there is one Fe3+ cation and three OH− anions.
Writing Formulas for Ternary Ionic Compounds
Writing a formula for a ternary ionic compound also involves the same steps as for a binary ionic compound. Write
the symbol and charge of the cation followed by the symbol and charge of the anion. Use the crisscross method to
ensure that the final formula is neutral. Calcium nitrate is composed of a calcium cation and a nitrate anion.
The charge is balanced by the presence of two nitrate ions and one calcium ion. Parentheses are used around the
nitrate ion because more than one of the polyatomic ion is needed. If only one polyatomic ion is in a formula,
parentheses are not used. As an example, the formula for calcium carbonate is CaCO3 . The carbonate ion carries a
2− charge and so exactly balances the 2+ charge of the calcium ion.
There are two polyatomic ions that produce unusual formulas. The Hg2 2+ ion is called either the dimercury ion
or, preferably, the mercury(I) ion. When bonded with an anion with a 1− charge, such as chloride, the formula
is Hg2 Cl2 . Because the cation consists of two Hg atoms bonded together, this formula is not reduced to HgCl.
Likewise, the peroxide ion, O2 2− , is also a unit that must stay together in its formulas. For example, the formula for
potassium peroxide is K2 O2 .
Summary
• Ternary compounds are composed of three or more elements.
• Ternary compounds are named by stating the cation first, followed by the anion.
• Positive and negative charges must balance.
Practice
Questions
Use the link below to answer the following questions:
http://www.youtube.com/watch?v=QNijl4ZBJCw
2
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Chapter 1. Names and Formulas of Ternary Ionic Compounds
MEDIA
Click image to the left or use the URL below.
URL: http://www.ck12.org/flx/render/embeddedobject/61210
1. What are ionic compounds containing polyatomic ions called?
2. Does the “criss-cross” method work for naming ternary compounds?
Review
Questions
1. What is a ternary compound?
2. What is the basic rule for naming ternary compounds?
3. Write the formulas for the following compounds:
1.
2.
3.
4.
mercury(II) nitrate
ammonium phosphate
calcium silicate
lead(II) chromate
4. Name the following compounds:
1.
2.
3.
4.
KClO3
Rb2 SO4
Cd(NO3 )2
NaCN
• ternary: A compound made up of three parts.
• ternary ionic compound: An ionic compound composed of three or more elements.
References
1. Jon Sullivan. Pizza .
2. CK-12 Foundation - Joy Sheng. Ca(NO3)2 Cross .
3