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Lets say I want to find the oxidation numbers of a formula.

For example:

$\ce{H3AsO3}$

Oxygen has a 2- charge. They're 3 of them, so its 6-

Hydrogen has a 1+ charge. They're 3 of them, so its 3+.

So Arsenic must have a charge of 3+ for all the charges to add up to be 0? Correct?

However, my professor keeps telling me to keep the positive oxidation numbers away from each other. Is that a rule when writing a formula?

I thought it only applied when drawing Lewis structures or resonance structures.

Thanks for your input.

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1 Answer 1

up vote 3 down vote accepted

Can two positive ions be next to each other in a formula?

Yes, there are many examples of this, $\ce{HNO3}$ for instance

So Arsenic must have a charge of 3+ for all the charges to add up to be 0? Correct?

Yes, that's correct

However, my professor keeps telling me to keep the positive oxidation numbers away from each other. Is that a rule when writing a formula?

It's not a rule that I'm familiar with. Here is a link to a nice, concise listing of the rules for writing formulas for inorganic compounds.

I thought it only applied when drawing Lewis structures or resonance structures.

Yes, it certainly applies in those two cases

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Ron, thank you for the clarity. –  Mark Jul 17 at 2:55
    
I think in $\ce{HNO3}\equiv\ce{(HO-)N(=O)2}$ no two positive partial charges are next to each other, so that would not provide an example, but $\ce{HNO}$ would. –  Martin Jul 17 at 2:55
    
So would you say that I can write $\ce{H3AsO3}$ as $\ce{AsH3O3}$ and it wouldn't make a difference because my Lewis diagram would remain the same? –  Mark Jul 17 at 2:58
    
@Martin I meant it in the nomenclature sense. In other words, in the molecular formula an $\ce{H}$ (+1) is written next to an $\ce{N}$ (+5) –  ron Jul 17 at 2:58
    
@Mark No, see the rules for constructing molecular formulas in the link I provided. –  ron Jul 17 at 3:00
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