How to Name and Write Polyatomic Ionic Compounds

By Sean Lancaster
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Naming ionic compounds in chemistry is important because it describes the chemical about which you are talking. For example, you may be discussing an experiment that results in the production of iron chloride. Using that name is not correct, because it leaves ambiguity as to whether you are producing iron(II) chloride or iron(III) chloride. Learning how to write an ionic compound's name, based on the naming conventions, is very important.

Examine the formula of the compound and take note of any ions present. If the ionic compound were dissolved in water, list the ions that would be present in the solution. For example, list the ions if Na2CO3 were dissolved in water. In this case, you should recognize sodium, Na+ as an ion with a +1 charge. The other ion will be CO32-, a carbonate ion with a -2 charge. Therefore, the ions in the solution would be Na+ and CO32-.

Ionic polyatomic compounds always state the name of the metal ion first. Evaluate the oxidation state of the metal ion, since many metal ions can exist in more than one oxidation state. Extending the example given, the first part of the name of the ionic compound is sodium, or Na+. Sodium has only one oxidation state, so in this case, no further work is needed. However, if the metal ion had been iron, you would need to find out which oxidation state, +2 or +3, it possessed in the ionic compound. In the case of a metal that exists in more than one state, you must express the oxidation state in the name of the compound. For iron, it would be either iron(II) or iron(III).

Write the name of the counter ions present in the compound. You will have to memorize many of the common anions, or negatively charged ions, in order to determine the counter ions present. Following the example further, the CO32- is the carbonate ion. The last part of the name is carbonate.

Link the two parts of the name together. Finishing the example, the name of the compound is sodium carbonate.

About the Author

Sean Lancaster has been a freelance writer since 2007. He has written for Writers Research Group, Alexis Writing and the Lebanon Chamber of Commerce. Lancaster holds a Doctor of Philosophy in chemistry from the University of Washington.