I recently came across a practice problem in my textbook asking me to name a few compounds using -ic and -ous endings. The exact wording is:

Write the name of each of the following ionic substances, using -ous and -ic endings to indicate the charge of the cation.

The first one was $\ce{CoCl2}$. However, cobalt has more than just two oxidization states (3, 2, 0, and -1).

So if it is one of the states in the middle, how do I decide whether to use -ous or -ic


1 Answer 1


Cobalt may possibly have all those other oxidation states (and others too) for this nomenclature system, we only care about the two most common oxidation states in ionic compounds: $\ce{Co^{2+}}$ and $\ce{Co^{3+}}$. Cobalt(II) compounds would thus be named cobaltous and cobalt(III) compounds would be cobaltic. Which is yours?

  • $\begingroup$ Chloride is -1 and it's Cl2 so Cobaltous. Thanks! $\endgroup$
    – 735Tesla
    Commented Jul 31, 2014 at 0:38
  • $\begingroup$ -1 as in the charge, not your answer. That was really helpful! +1 $\endgroup$
    – 735Tesla
    Commented Jul 31, 2014 at 0:38
  • $\begingroup$ Is there a reference you would recommend for finding the most common oxidization states? I can't find one in my book and online. $\endgroup$
    – 735Tesla
    Commented Jul 31, 2014 at 1:59
  • 1
    $\begingroup$ $\ce{Co^3+}$ oxidizes $\ce{Cl-}$. I know this from personal experience. $\endgroup$
    – A.K.
    Commented Aug 17, 2018 at 0:25
  • $\begingroup$ Depending on its ligands Co3+ might oxidize Cl- is closer to the truth $\endgroup$
    – Ian Bush
    Commented Aug 17, 2018 at 6:11

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