The short answer is that 'oxidation states' are simply a formalism that do not really describe reality very well. They are just the numbers you get by adding up the charges you predict for an atom if:

1) you consider only the electronegativities of the individual atoms

2) all bonding is only ionic

Both of these assumptions miss significant effects. For (1) the electron density on an atom certainly is affected by what its bound to. For (2) it is pretty clear that chemical bonds are never only ionic in character (even Cs-F has some small amount of covalency)

Essentially, oxidation states are just used as an accounting tool to keep track of electrons and should not be taken too seriously as descriptions of reality.

If you do wish to have a good understanding of the bonding in molecules then MO theory is really what you need to use.

The short answer is that 'oxidation states' are simply a formalism that do not really describe reality very well. They are just the numbers you get by adding up the charges you predict for an atom if:

1) you consider only the electronegativities of the individual atoms

2) all bonding is only ionic

Both of these assumptions miss significant effects. For (1) the electron density on an atom certainly is affected by what its bound to. For (2) it is pretty clear that chemical bonds are never only ionic in character (even Cs-F has some small amount of covalency)

Essentially, oxidation states are just used as an accounting tool to keep track of electrons and should not be taken too seriously as descriptions of reality.

If you do wish to have a good understanding of the bonding in molecules then MO theory is really what you need to use.

Hello,

I am trying to give goosd explanation.

Na2S2O3

Oxidation state of 'S' you do not know, ok

Oxidation state for sodium = 1, So, Two sodium gets (1+1)= 2

Your question is oxidation state for sulphur, So unknown, There are two sulphur atoms are there, we will write as 2x

Oxidation state for oxygen = -2.There are there are three oxygen atoms, So

                                              (-2*3)= -6

Just apply in the avove molecular fomula,

Na2S2O3

(2+2x-6) = 0

(2-6)+2x= 0

-4+2x= 0

x " means sulphur atom = 2, So

Osidation state of sulphur is "2"

Thanks and regards,

prabhu

hello Ian,

Its true that the concept of oxidation state assumes that the bond and the definition of oxidation state covers this assumption. Although it does not give the real picture but it tells about the number of electrons shared and it they shifting towards or away from any atom.

The true answer -2 and +6,  This molecule was  formed by by replacing of one osygen atom into sulfur in the acidic residue

This is a same question which had answered by my teacher  long back. I will only try to answer this and hope you will be satisfied with it.And this not a question but a querry.

Your querry is valid provided your looking it in right direction.

Sulfur exists in +6 and -2 in thiosulfate anion. which you will agree. so once again revise the following

In case of sulfate anion, there are four oxygen atom and it is tetrahedral anion having (SO4)2- charge. So you will agree that sulfur is in +6 oxidation state.

Now consider sulfur trioxide SO3 which has a plane structure with +6 . It exists as gas but an acidic gas. Now if the gas is passed in water you will get H2SO4. Here your argument will hold good as per electronegativity concept here water does that trick by lone pair of electrons.

To the acid if you add base you will get sodium sulfate.

H2S is also a gas but weak dibasic acid type and to this if you add base it it will become S2- and SH-.

Thiosulfate will exist in slighlty alkaline medium. And if you make the pH acidic sulfur will be thrown out causing +6 and -2 reactivity.

Your question is valid and that is why  thiosulfate anion is not stable in acidic, ie H2(S2O3) and also H2S being a gas it will either escape from solution in acidic medium or will form sulfur medium and I hope this will answer the question.

I see that this is an old question, but any of those interested may want to check out this older article from Vairavamurthy and colleagues. When you run x-ray absorption spectroscopy on thiosulfate, two peaks comes out that appear to correspond primarily to the 1- and 5+ oxidation states of sulfur, though 4+ and 6+ oxidation state peaks will be there as well. It's very interesting. I read a paper some time back (can't recall the authors) who claimed that these peaks can't possibly be 1- and 5+, but they didn't offer an explanation for why all of us who do XAS on thiosulfate get those peaks (they are very standard).

http://www.sciencedirect.com/science/article/pii/001670379390020W