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Liquids - simple question

  1. May 22, 2010 #1
    Hi
    Why liquids behave as they do?
    I mean many sloids have density greater than some liquids e.g ice - water but still ice is solid and water liquid. This means flowability doesn't depend only on density. Then on what it depends?
    I mean how will you answer that why is this/that substance a liquid.
     
  2. jcsd
  3. May 22, 2010 #2

    mgb_phys

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    It all depends on the bonds between the atoms/molecules of the substance.
    In a solid they are strongly attached to each other, crystals eg diamond, have the strongest bonds between atoms and are the most solid-like of solids. Graphite has weaker bonds and so is softer and behaves a little more like a liquid.

    In liquids there are only very weak bonds between different molecules
     
  4. May 22, 2010 #3
    why water expands when cooled or why ice contracts when given heat?
    on giving heat moleclules should slip away from each other and density should decrease!
     
  5. May 22, 2010 #4
    Because of formation of hydrogen bonds.When water is cooled to 4°C, the molecules get close enough that a hydrogen atom of one molecule is bonded to oxygen of another as they develop partial charges due to difference of electronegativity.The molecules rearrange according to the bond energy as the sample goes on cooling.
     
  6. May 22, 2010 #5

    mgb_phys

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    Water is rather odd - it's the only material that expands when frozen, due as vin says, to hydrogen bonds.
     
  7. May 22, 2010 #6
    All "super cooled liquids" contract with heat and expand when cooled.
    Glass is a super cooled liquid with the same properties as water where heat and expansion is concerned.
     
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