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Polyatomic ions and their charge

  1. Aug 29, 2011 #1
    This question is regarding polyatomic ions and their charge. I have always been told that I have to memorize the charge of polyatomic ions. The question is whether I can determine by myself the charge of two atoms when they join together to form a polyatomic ion. For example Se and O can form selenate SeO4, this polyatomic ion has a charge of -2. I would like to know why is the charge -2? But what I know the sum of all oxidation states of the joining ions must be equal to the net charge of the ion. But what happens then if I do not know the net charge of the ion? Hopefully these questions are not too silly. Thanks before hand, Aldo.
  2. jcsd
  3. Aug 29, 2011 #2

    Because the ion is like this. There is 1 unpaired electrons on 2 oxygen atoms, giving it a charge of 2-.

    For these kinds of ions, just try pairing up their electrons to get a stable electron configuration until you only have unpaired electrons left. You can then deduce the charge of the whole ion from that.
  4. Aug 29, 2011 #3
    Ok, seeing the bonds in the ion helped. Thank you very much for your help. So, when I have the SeO3 anion with a charge of -2, I would have 1 Selenium Oxygen double bond and two Selenium Oxygen single bonds, with an electron pair in the Selenium? Aldo.
  5. Aug 29, 2011 #4

    btw, what's aldo?
  6. Aug 29, 2011 #5
    Thanks again for your help. Hahahaha..Aldo is just my name : )
  7. Oct 24, 2013 #6
    I still don't get how SeO4 acquires a charge of 2-. I don't understand the diagram above either. Please explain in more plain language.
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