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Boiling point comparison between of H2S, H2Se, H2Te

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Donchacka

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So the actual trend here is H2S<H2Se<H2Te. What I dont understant is that H2S has the strongest dipole dipole interaction and since dipole-dipole interaction is stronger than dispersion force, H2S really should have higher boiling point than H2Se but why is it the opposite?
 

Thoroughbred_Med

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So the actual trend here is H2S<H2Se<H2Te. What I dont understant is that H2S has the strongest dipole dipole interaction and since dipole-dipole interaction is stronger than dispersion force, H2S really should have higher boiling point than H2Se but why is it the opposite?

Forget about the intramolecular forces so much. I would give more attention the different molecular weights... as they are significant... there is almost a 100% increase as you go from H2S<H2Se<H2Te.
The heavier the molecule, the higher the boiling point.

You are not wrong for looking at the intramolecular forces, but look at the weights first. Hope this helps.
 

vivatix

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Since S, Se, Te are in the same group of the periodic table - so they have the same type of forces/bonding. In this case, look at the molecular weight.
HTe has the highest molecular weight and thus it has the highest boiling point.
 
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