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Common polyatomic ions

Reviewing the common polyatomic ions, and explaining common suffixes and prefixes to help remember the formulas.  Created by Jay.

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  • male robot hal style avatar for user Mirghani
    why is acetateis CH3COO
    isn't it proper to write C2H3O2?
    (28 votes)
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  • piceratops seed style avatar for user Amber Lancaster
    Is there a way of determining their names without memorizing the other polyatomic ions?
    (15 votes)
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  • marcimus pink style avatar for user miss nailah
    Im confused on how you know when to put the ending "-ate" or when to put "-ite".
    At around you said that is depends on iff it has more or less oxygens, so does that mean that if it had 4 oxygens it would be "-ate"?
    So do you start using the ending "-ate" when you have more than 2 oxygens?
    (15 votes)
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  • blobby green style avatar for user Joe Luker
    Are there any examples of oxyanions that have only three oxidation levels? If so, as far as terminology, should we use ("hypo"-"ite"-"ate") or ("ite"-"ate"-"per")?
    (8 votes)
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    • starky ultimate style avatar for user Ray Bunten
      For me the key is remembering at least one oxyanion for each element pairing, and then use the naming convention from there. The key is to say, "I know what this one is, and I can find the ones around it by going up to "-ate" then "per"+"ate", or down to "ite" and "hypo"+"ite"."
      (2 votes)
  • blobby green style avatar for user Sargent René Léonce
    why does it seem that the ionic compounds here are unbalanced?
    (7 votes)
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  • female robot grace style avatar for user S. Carr
    I see that the "ate" and "ite" mean more and few oxygen, respectively; but what am I comparing it to? More/fewer oxygen that what?
    (3 votes)
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    • spunky sam blue style avatar for user Ernest Zinck
      You are comparing them to each other.
      If you have two salts of oxyacids whose formulas differ by only one oxygen atom, the one with one more O atom is an "ate" and the other one is an "ite".
      Thus, Na₂SO₄ is sodium sulfate and Na₂SO₃ is sodium sulfite.
      NaNO₃ is sodium chlorate and NaNO₂ is sodium chlorite, etc.
      At this stage, all you can do is memorize the "ates" and then you can figure out the "ites".
      (8 votes)
  • orange juice squid orange style avatar for user wolfiehomeschool716
    why is there more anions than cations?
    I just don't get it
    (4 votes)
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  • hopper cool style avatar for user Ritvik‮
    Why is it CH₃COO- instead of C₂H₃O₂-? Don't the elements that are the same combine? Or is it something to do with the structure of the ion?
    (4 votes)
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    • piceratops seed style avatar for user RogerP
      Writing it as CH3COO- makes more sense from a structural point of view. This is the acetate ion which is formed when acetic acid (CH3COOH) loses its proton. Both these molecules contain a carboxyl group, which can be depicted as a carbon double bonded to one oxygen and single bonded to another oxygen (O=C-O-) and which is usually written as COO- (or sometimes as CO2-).

      A chemist seeing CH3COO- written down will instantly know that this is acetate whereas C2H3O2- isn't immediately recognisable as acetate.

      Writing it as C2H3O2- isn't wrong, but it is unconventional.
      (4 votes)
  • duskpin sapling style avatar for user TanishTanay
    why is acetateis CH3COO
    isn't it proper to write C2H3O2?
    (4 votes)
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  • duskpin ultimate style avatar for user Sophie
    Hello! I have a few questions: Can hydrogen phosphate also be called biphosphate? Like when we added Hydrogen to Sulfate, we got hydrogen sulfate, which is also known as bisulfate. And the same happens with carbonate... So if we add Hydrogen to any charged ionic compound, we keep the name of the original compound (for example sulfate), and then add "bi" (like bisulfate)? And what is the difference between the prefixes "bi" and "di"? Like could we call dihydrogen phosphate, bihydrogen phosphate? Can we call dichromate as bichromate? Both "di" and "bi" mean 2 right? And if we can't, why not? Also Chromate has 1 chromium atom, and 4 oxygen atoms. But then dichromate has 2 chromium atoms, and 7 oxygen atoms... why are there 7 oxygen atoms? I thought that only the number of chromium's were supposed to double... Also, what exactly are these? Like I read that ionic compound's charges must cancel, but here we have anions and cations? There can be ions with charges that form substances but aren't considered compounds? So if atoms get attached to each other, gain or lose electrons, they are in an ionic bond, but they don't form a compound, but can form a substance? Then for example what is ammonium? Is it a compound or an ion? If it is an ion, then shouldn't it also be a compound?... I am a bit confused.......
    Thank you
    (4 votes)
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Video transcript

- [Voiceover] When you take a general chemistry class, you often have to memorize some of the common polyatomic ions. So let's go through a list of some of the ones that you might see in your class. So we'll start off with Cation here, so a positively charged ion, NH four plus is called the Ammonium ion. And for Anions, there are many Anions that you should know. CH three COO minus is the Acetate ion. CN minus is the Cyanide ion. OH minus is the Hydroxide anion. MnO four minus is the Permanganate ion. And, when you get to NO three minus versus NO two minus, look at the endings. So NO three minus is Nitrate, so we have ate suffix, ate suffix here, which means more Oxygens. Versus the ite suffix, which means fewer Oxygens. So we can see that Nitrate has three Oxygens and Nitrite has two Oxygens. And that ending is important because it's gonna help you with some of the other polyatomic ions. For example, let's look at this next set here of four. And let's look at Chlorate. So Chlorate has three Oxygens. It's ClO three minus one. And Chlorite has fewer Oxygens, it has two Oxygens here, ClO two minus. So we have ate meaning more and ite meaning fewer here. What about Perchlorate? So here we have Chlorate, but we've added on a prefix this time and the prefix, per, means one more Oxygen. So Perchlorate means one more Oxygen than Chlorate. Chlorate had three Oxygens and for Perchlorate we add one on and we get four. So Perchlorate is ClO four minus. Next, let's look at Hypochlorite. So we talked about Chlorite up here, so here's Chlorite and then we put a prefix, hypo, in front of it. Hypo means one fewer, so if we look at Chlorite, we had two Oxygens, we take one away and now we have only one Oxygen. So that must be the Hypochlorite ion. We could have done this for a different halogen, here we're dealing with Chlorine, but let's say, instead of ClO three minus, let's do BrO three minus. ClO three minus was Chlorate, here we have Bromine instead of Chlorine, so this would be Bromate. So there's another polyatomic ion and we can do another example. So instead of ClO minus, which is Hypochlorite, we could have had BrO minus, which would therefore be Hypobromite. So this would be Hypobromite. Alright, let's look at our next set of polyatomic ions. Alright, so let's get some space down here. So we have SO four two minus, is called Sulfate. Right, so we have our ate ending. And then we have four Oxygens, so if we go to three Oxygens, SO three two minus, this is Sulfite, cause ite means fewer Oxygens. What about if we took Sulfate, SO four two minus, and we added on an H plus. So H plus and SO four two minus should give us HSO four and then, instead of a negative two here, instead of a two minus, we would just have a one minus, because we added on a positive charge. So one positive charge and two negative charges, give us one negative charge. So HSO four minus is called the Hydrogen Sulfate ion. You might also hear Bisulfate for this one. Next CO three two minus is called Carbonate, so if we add on an H plus to CO three two minus, we'd get HCO three and then we go from minus two or two minus, to minus one, 'cause we're adding on a positive charge here. So HCO three minus is called Hydrogen Carbonate and you'll also hear Bicarbonate a lot. Next we have PO four three minus, which is called Phosphate. If we add on an H plus to Phosphate, think about what we would get. We would get HPO four and then instead of three minus, we're adding on positive charge, so we get two minus. So we call this Hydrogen Phosphate. Alright, let's add on a proton to Hydrogen Phosphate. So we're adding an H plus onto Hydrogen Phosphate. That would give us two H's. PO four and we'd go from two minus down to one minus. So H two PO four minus is called Dihydrogen Phosphate. Alright, let's continue on. One more set of polyatomic ions to know. So we have CrO four two minus, which is called Chromate. And if we have two Chromiums, so Cr two O seven two minus this is called Dichromate. Next, C two O four two minus is called the Oxalate ion. and we have O two, two minus is called Peroxide. And here we have SCN minus, which we call Thiocyanate. So thio, think about sulfur if you see thio there. So for our next one, we have sulfur present again, is S two O three two minus and this one's called Thiosulfate. So you might see a few additional polyatomic ions in your class, but these are the ones that you see most frequently. So make sure to memorize your polyatomic ions.