Compare H2O and H2S

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Compare H2O and H2S

Postby Chem_Mod » Sun Aug 21, 2011 11:55 am

According to the solution manual H20 is more basic or is a stronger Lewis base than H2S because oxygen is more electronegative than S and has a higher partial negative charge. But if O is more electronegative than S, wouldn't that mean that O has a greater pulling force of electrons than S? And if that is the case, then shouldn't the O in H20 have a greater resistance in donating the lone pairs, which contradicts the Lewis base definition of being an electron donor? So therefore, H2S should be more basic than O because S is less electronegative, which means that it is easier for H2S to lose its electrons and become an electron donor?

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Re: Compare H2O and H2S

Postby Chem_Mod » Sun Aug 21, 2011 11:56 am

Your reasoning is correct but there are more factors that determine e- pair availability and it turns out that H20 is more basic. Clearly their is a balance between the larger negative charge and the availability of the lone pairs. In the case of H20 versus H2S, the larger negative charge favors H20 being more basic.


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