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Thread: Hydrogen bond

  1. #1 Hydrogen bond 
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    i want to fing out why ice float on the water.
    everybody know the electron is negative and proton is positive.when 2 hydrogen covalently bonded with oxygen,it become water.the oxygen is more electronegative than hydrogen.
    some website:
    the oxygen atom attract the shared pair of electron toward itself so it get partial negative charge.hydrogen got partial positive charge.
    but,positive attract negative.why negative(oxygen atom) attract negative(shared pair of electron.??
    the formation of hydrogen bond need hydrogen atom..i don't, why the hydrogen bonds cannot form between Carbon and 2 oxygen....?
    lastly,1 hydrogen bond form between NH3 and NH3..sowhen it become solid..it has a few hydrogen between them.how to draw the solid state of NH3..
    there are 3.4hydrogen bond between water molecule whenit is liquid state.3.4????How to say this..i cannot understand...


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  3. #2  
    Forum Freshman Sudhamsu's Avatar
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    Ice floats on water simply because its lighter than the same volume of water, that is it is less denser than water. Gravity tries to pull down the ice, but buoyant force of the water keeps it floating. Read: http://en.wikipedia.org/wiki/Buoyant_force

    For your second question, the oxygen atom is neutral in the beginning and it gains negative charge after making the bond with hydrogen atom. Even after gaining some negative charge, the nucleus in the oxygen still has strong enough effective positive charge, that is the nucleus can still attract more electrons. (Oxygen is most electronegative after fluorine.)

    I don't think you've got the right picture of the Hydrogen Bond. Any bond between an atom and a Hydrogen atom is NOT a Hydrogen Bond. A hydrogen bond is that bond between an atom of a molecule (neutral or not) and the Hydrogen atom of another molecule (or in some cases the same molecule.) This bond is not a normal covalent or ionic bond. The Hydrogen atom is very electro-positive, hence it usually bears positive charge, this can attract some negative charge from electronegative atoms like oxygen, nitrogen and fluorine. This results in a weak linkage between the two atoms (hence molecules). The Hydrogen bond is weaker than covalent or ionic bonds, but stronger than the van der Waal's interactions. This type of bonding is almost exclusive to the Hydrogen atom-Oxygen/Nitrogen/Fluorine atom, hence the name. There can also be some similar interaction between carbon and oxygen, of nitrogen and oxygen, but these are almost of the same electronegativity, hence the interactions are not strong, and are negligible.
    Read: http://en.wikipedia.org/wiki/Hydrogen_bond

    In water, in its liquid form, a single water molecule has one oxygen atom and two hydrogen atoms. The oxygen atom (lets say of Molecule 1) has lot of negative charge on it. This can attract both of the hydrogen atoms of another adjacent water molecule (Molecule 2). And also there can be another oxygen atom of Molecule 3 which attracts the two hydrogen atoms on Molecule 1. Hence the Molecule 1 is participating in 4 hydrogen bonds. Draw the described arrangement on a sheet of paper to understand it better. (i.e. Molecule 3 <=> Molecule 1 <=> Molecule 2)

    Hope this helped...


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  4. #3  
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    thank you very much..i hope i can always discuss with you about physic and chemistry..
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