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Chemistry Forums for Students => High School Chemistry Forum => Topic started by: AppleSnooop on November 10, 2019, 10:30:25 PM

Title: Is there anyway to memorize common polyatomic ions easily?
Post by: AppleSnooop on November 10, 2019, 10:30:25 PM

I have a polyatomics quiz in a couple days, my teacher has given us about 15 polyatomics to memorize and I can't do it for the life of me. Is there a certain pattern? Trick?

Title: Re: Is there anyway to memorize common polyatomic ions easily?
Post by: isaackrementsov on November 11, 2019, 12:45:27 AM

Yes. Although there are a lot of exceptions, the general rule for oxyanions (most polyatomic ions you probably have to memorize) is:
-ate = Some element with some number of oxygens, usually 3. Ex: Chlorate = ClO₃^-
-ite = The same element with one less oxygen. Ex: Chlorite: ClO₂^-
hypo- ... -ite = One less oxygen than -ite. Ex: Hypochlorite: ClO^-
per- ... -ate = One more oxygen than -ate. Ex: Perchlorate: ClO₄^-
Changing the number of oxygens in the anion will not change the charge.

Also
Bi-/Hydrogen- = The original ion with a hydrogen attached. Ex: Bisulfate/Hydrogen phosphate = HPO₄^2-
Prefix + Hydrogen- = The ion with some number of hydrogens attached. Ex: Dihydrogen phosphate = H₂PO₄^-
Every hydrogen added will increase the ion's charge by 1.

Other than that, I recommend just creating or running through an existing Quizlet. There are a lot of strange patterns, even with oxyanions, and you do have to remember where the -ate ion is before knowing any of the other forms.

Hope this helped.