Knowing the range of oxidation states

[deleted647690]

Is there a way to figure this out for any given element? For example, I just did a question that required knowing that Sulfur, in its -2 oxidation state, is considered fully oxidized. From the answer, I know that Sulfur can range from -2 to +6. I guess +6 could come from knowing that it has 6 valence electrons since it is in the 16th column of the periodic table.


I guess looking at its electron configuration, 1s22s22p63s23p4, you can tell that it can accommodate an additional 2 electrons in the 3p orbital?

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[aldol16]

I think you mean fully reduced. An easy way to do this is look and see the two ways it can form a full octet. Atomic sulfur can either gain two electrons and end up with Ar's electronic configuration or lose 6 electrons and end up with Ne's configuration. Putting an additional electron onto sulfur after it has reached Ar configuration is unfavorable, even given expanded valence. Similarly, taking an additional electron from sulfur after it has reached Ne configuration is unfavorable.

 

[deleted647690]

I think you mean fully reduced. An easy way to do this is look and see the two ways it can form a full octet. Atomic sulfur can either gain two electrons and end up with Ar's electronic configuration or lose 6 electrons and end up with Ne's configuration. Putting an additional electron onto sulfur after it has reached Ar configuration is unfavorable, even given expanded valence. Similarly, taking an additional electron from sulfur after it has reached Ne configuration is unfavorable.

Yeah, I should have said reduced. So with you reasoning, with any element, the oxidation state can range from any value between where it would be oxidized/reduced to the next nobel gas? Meaning, for S, it can either lose 6 electrons and get to Ne or gain 2 electrons and get to Ar. So it can range anywhere from -2 to +6 (so oxidation state can range from gain of two electrons to loss of 6 electrons)

 

[aldol16]

Yeah, I should have said reduced. So with you reasoning, with any element, the oxidation state can range from any value between where it would be oxidized/reduced to the next nobel gas? Meaning, for S, it can either lose 6 electrons and get to Ne or gain 2 electrons and get to Ar. So it can range anywhere from -2 to +6 (so oxidation state can range from gain of two electrons to loss of 6 electrons)

Yes, these are good general guidelines for non-transition metal elements. For transition metals, the d-orbital filling governs oxidation state and d-orbitals have more complexity than the MCAT could ever test on. But also use your chemical sense. Something like Na isn't going to gain 7 electrons just to reach noble gas configuration. Similarly something like fluorine isn't going to lose 7 electrons. Gaining one electron is much easier.

Something like sulfur can lose six electrons because the electrons it's losing are in the more loosely held n = 3 shell.