Naming Polyatomic Ions

How to Name Polyatomic Ions

Here are some simple rules for naming polyatomic ions.

Polyatomic ions with more oxygen atoms will end in -ate, and those with fewer oxygen atoms will end in -ite. When there are more than two polyatomic ions composed of the same elements, the prefix hypo- indicates the least number of oxygen atoms, and the prefix per- will indicate the most oxygen per ion.

Less Oxygen More Oxygen
hypo- -ite -ate per-

Look at the paradigm for chlorine oxyanions below.

Click in the name column to reveal, or highlight on phone or tablet.

Formula Name
ClO⁻ Hypochlorite
ClO₂⁻ Chlorite
ClO₃⁻ Chlorate
ClO₄⁻ Perchlorate

Frequently, common ions you will need to know for class will only include two configurations, one in -ite and one in -ate. You will still have to memorize how many oxygen are in each on a case-by-case basis.

Here’s a video from Youtuber PCNB with a visual way to remember how many oxygens and what charge each ion ending in -ate has. After you learn the pattern for -ates, you can just use the pattern above to figure out -ites and the rest!

Other things to know:

Prefix di- means two (of the first element in the ion).

E.g. Cr2O72- = Dichromate

Hydrogen carbonate and hydrogen sulfate are also known as bicarbonate and bisulfate.

How to Name Compounds with Polyatomic Ions

It’s fairly simple if you know the name of the ion! Each compound will have a first name and a last name. If the polyatomic ion has a negative charge (which is more common), the last name will be the name of the ion. The first name will be the name of the first part (cation), or what’s left. In the simplest case, this first name will just be the name of a single element.

Name a compound by reading left-to-right. So if we have a compound with a positive ion like ammonium, such as NH4NO3, the name would read ‘ammonium nitrate.’

Click on the name to reveal, or highlight on mobile.

Formula Name
KClO3 Potassium chlorate
SnSO4 Tin sulfate
Cu(ClO3)2 Copper (II) chlorate
Pb(NO3)2 Lead (II) nitrate

Here’s a video from YouTuber MsLuckyChemist where she explains a few examples of polyatomic compounds. She refers to her own class’ polyatomic ions list–you can use ours by clicking here.

Practice Naming Polyatomic Ions

Our free online memorization games at Study Putty give you a few ways to practice the names and charges of polyatomic ions. Try the simple “Drag & Drop” (screenshot below) to match common polyatomic ions to their names.

Naming polyatomic ions (a Study Putty game)

About Bret Norwood

Bret Norwood is a staff blogger for Learning Laboratory in addition to other roles, including UI design and content development for Study Putty, our free memorization tool for chemistry and many other course topics. He is also a published writer of literary fiction–see BretNorwood.com

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