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why does H2O have a higher melting point than H2S when H2S is covalently bonded ? covalent bonds are stronger than hydrogen bonds and therefore, would need more energy to break, but H2O has a higher melting point.
Both H2O and H2S have covalent bonds between their hydrogen atoms and their oxygen or sulfur atoms, but in H2O there are also hydrogen bonds between the hydrogen atoms and oxygen atoms of different molecules. These hydrogen bonds between molecules, in addition to the covalent bonds within each molecule, are what cause the higher melting point.
Hydrogen bonds can exist between hydrogen and nitrogen, oxygen, or fluorine atoms. Because H2O possesses hydrogen bonds in addition to covalent bonds, it can stick together better than H2S. Therefore, it has a higher melting point.
Covalent bonds are intramolecular bonds (bonds within a molecule) whereas hydrogen bonds are intermolecular bonds (bonds between molecules). In H2O the bonds between the different H2O molecules are hydrogen bonded, but in H2S the H2S molecules are bonded with a dipole dipole interaction because hydrogen bonds are only formed between hydrogen and either oxygen, fluorine, or nitrogen. So since dipole dipole bonds are weaker than hydrogen bonds, this results in water having a higher melting and boiling point because it is harder to break those bonds.
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