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Normally, water is a liquid but hydrogen sulphide a gas. Why?

  1. Oct 27, 2016 #1
    • You have to show your attempts at answering the question, this is a forum policy. Also, all homework like questions should go to homework forum.
    The accepted explanation for the existence of water as a liquid involves hydrogen bonding. Why is this phenomenon absent in the case of hydrogen sulphide?
     
  2. jcsd
  3. Oct 27, 2016 #2
    • Instead of giving full explanations, please help the OP to find the answer on their own. Just asking what factors affect the hydrogen bonding in hydrogen sulfide and whether it is stronger or weaker in water would point the OP in the right direction.
    oxygen has smaller size and higher electronegativity than Sulphur. This results in strong H- bonding which does not exist in Sulphur.
     
  4. Oct 28, 2016 #3
    Unsure why a drop of just under 1 in electronegativity from oxygen to sulphur compensates for the difference in molecular weight between water and hydrogen sulphide.
     
  5. Oct 28, 2016 #4

    Borek

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    "Just under 1"? What is the range of the electronegativity changes in general?
     
  6. Oct 28, 2016 #5
    From just under 1 to under 4; with oxygen at 3.44 and sulphur at 2.58.
     
  7. Oct 28, 2016 #6

    Borek

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    This is NOT a small change.

    Especially when accompanied by the change in the radius.
     
  8. Oct 28, 2016 #7

    James Pelezo

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    There are three types of 'Bonds' ... Physical, Chemical and Nuclear. To better understand this issue, you should review 'Physical Bonds' and how they are related to 'Chemical Bonds' especially as they apply to the interaction of Molecular Compounds and 'State of Existence'; i.e., solid, liquid or gas states ... Terms like Electronegativity, Bond Polarity, Molecular Polarity, Partial Charges, Formal Charges, Resonance and Molecular Geometry should be reviewed to develop a complete picture of what's happening on the molecular level particle-particle interactions. Good luck.
     
  9. Oct 28, 2016 #8

    Borek

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    Not sure what you are referring to, but I am more than sure that whatever you mean by each they are just ends of a bond continuum, and it is possible to give examples that lie exactly in between.
     
  10. Oct 28, 2016 #9

    James Pelezo

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    The original question was why is water liquid, but H2S is gas (i.e., doesn't demonstrate H-Bonding as does HOH) under the same conditions (i.e., 25oC; 1 atm)? To answer that question one needs to understand how chemical bonds, physical bonds and properties of the elements and molecules interact. You are right, it is a continuum of factoids drawn from each topic listed. Was just trying to make a suggestion of what should be reviewed to answer such questions.
     
  11. Oct 31, 2016 #10

    epenguin

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    I think you have got answers that are good enough for your purposes.

    I am not an expert on this, but I know that some people consider the inability of -S-H to participate in the hydrogen bonding is often exaggerated. Water structure is a complex subject; I think this passage is suggesting that cooperative phenomena involving extended hydrogen bonded and structures with several molecules of water play a part. https://books.google.it/books?id=p1...QggMAA#v=onepage&q=Hydrogen bonds H2S&f=false
    And that just the different bond angles in H2O and H2S cause an inability to form the larger structures in H2S.

    Hydrogen bonded structures involving -S-H of cysteine residues are known in proteins. http://web.unbc.ca/~rader/_publications/1991Gregoret.pdf .

    So in more advanced studies and different contexts this absolute difference between the two atoms will be relativised - but till then what you have heard so far is much what you will hear. There is some nice pictorialisation and connection with other physics and biology here: http://www.slideshare.net/chungkin81/hydrogen-bonding.

     
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