Explain why water has higher boiling and melting point as compared to H2S ?(PLs ans URGENTLY)

1 Answer
Oct 13, 2016

This is a result of the significant hydrogen bonding present in the water molecule.


Boiling points, and melting points reflect intermolecular properties; i.e. the interactions between particles, between molecules. In water, the hydrogens are bound to oxygen, a strongly electronegative element. The oxygen atom polarizes electron density away from the bond to give #"^(delta+)H-O^(delta-)-H^(delta+)#. This charge separation, this polarity, operates in the bulk phase as an additional intermolecular force, and results in unusually high melting and boiling points for water.

Of course, hydrogen sulfide is isoelectronic, and isostructural with the water molecule, however, the degree of hydrogen bonding in #H_2S# is of MUCH lower magnitude for this molecule; sulfur is LESS electronegative than oxygen on account of its 3rd period placement. The result? #H_2S# has less intermolecular interaction, and the material is a room temperature gas.