I have had the case a few times. Being given something of this form:
$$\ce{Cr2O7^2-}$$
How do I know whether the $2-$ is referring to the oxidation of the oxygen anion or the charge of the whole compound?
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asked Jan 11, 2016 at 18:55
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1$\begingroup$ Because charge is written like that? $\endgroup$– MithoronCommented Jan 11, 2016 at 19:00
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$\begingroup$ So you never write oxidation state in the upper right corner? $\endgroup$– LandonZeKepitelOfGreytBritnCommented Jan 11, 2016 at 19:03
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1$\begingroup$ en.wikipedia.org/wiki/Oxidation_state $\endgroup$– MithoronCommented Jan 11, 2016 at 19:13
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$\begingroup$ Oxidation state: first the sign then the number: -2. Charge: first the number then the sign: 2-. $\endgroup$– EJCCommented Jan 11, 2016 at 20:20
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$\begingroup$ @Marko Roman numerals are used in formulas and names, so there's no mistake. $\endgroup$– MithoronCommented Jan 12, 2016 at 0:04
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1 Answer
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make sure to read up about that topic. The concept of charge and oxidation state are closely related but aren't the same.
Usually oxidation state is written with roman numbers (that's how I learned it) and are not explicitely written like in the example you showed.
Charges on the other hand are always written (if mentionned) on the upper right side of the anion.
I am far from being an expert, but thinks this might be an answer to your question.
answered Jan 11, 2016 at 19:06
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$\begingroup$ Superscripted Roman numerals are (I think?) a somewhat newer notation, but are in my experience becoming quite common. $\endgroup$– hBy2PyCommented Jan 11, 2016 at 21:23