Dissociation of different compounds?

What would be the dissociation of Hydrosulfuric acid in the presence of water?


I was thinking that Hydrosulfuric acid or $\ce{H2S}\_{(aq)}$ would form $\ce{2 H+}$ and Sulfur ions.


With this logic, I keep getting the wrong answer :(


The right answer of this question is it would not dissociate at all.


Shall appreciate some help on explaining this. Thanks!




[$\ce{H2S}$](http://en.wikipedia.org/wiki/Hydrogen_sulfide) has a mostly covalent character. You can decide for it by the crude way textbooks give: Calculate the difference in electronegativity to decide whether it's a non-polar covalent compound, a polar one or has ionic characters.


For the dissociation part (which is usually endothermic overall) it'll need more "ionic character". And it *does* dissociate in water, resulting in a weak acid named sulfhydric acid. (The spelling varies with citable sources) Your textbook likes to think about it as not dissociable, only because it's a **weak acid**.


Addendum:
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The "ionic character" plays its role of a rule a good one as explaining acid 'strength'. However, it acts almost flawlessly in the same period, but has exceptions when it gets to groups. As Dave mentions, $\ce{HF}$ is weaker than for instance, $\ce{HCl}$ and that's because **the atomic radius changes more dramatically than electronegativity difference**. (See [here](http://drholly.typepad.com/ask_me_a_chemistry_questi/2005/12/why_isnt_hf_a_s.html) ) But, in the $\ce{H2S}$ molecule, this exception hasn't occurred. Dave pointed out a good example of when the rule isn't working that well, but as I said, we can ignore the other factors in this very case.


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