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Why does the melting point of graphite is higher than diamond?

  1. Jul 13, 2013 #1
    In diamond valence electrons are fully covalently bonded.But in graphite only three are covalently bonded while one electron is freely moving.So it seem that melting point of diamond should be higher than that of graphite because in diamond we should break four covalent bonds while in graphite only three bonds.Can anyone explain this pls?
     
  2. jcsd
  3. Jul 13, 2013 #2
    The melting point of graphite is slightly larger than the melting point of diamond, because in graphite C-C bonds have a partial double bond character and hence are stronger and more difficult to break.

    There are also Van der Waals forces between the layers of graphite but these are relatively weak in comparison to a covalent bond. These weak forces allows layers of graphite to slide past each other...
     
  4. Jul 16, 2013 #3
  5. Jul 16, 2013 #4
    What are you claiming graphite´s melting point to be? It is still remarkably hard to measure!
     
  6. Feb 19, 2014 #5
    why does the melting point of graphite is higher than diamond? I have the same problem. please can anyone explain this?
     
  7. Feb 19, 2014 #6

    adjacent

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    This thread is more than 6 months old.
    Please read the above posts.
     
  8. Feb 22, 2014 #7
    So starting with the same question: what do you claim graphite melting point is?
     
  9. Feb 22, 2014 #8
    Diamond doesn't even melt, it burns. Even still the "melting" point of diamond is 4300K whereas graphite is 3948K
     
  10. Feb 22, 2014 #9

    adjacent

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    Corrected :wink:


    It is possible to melt diamonds. However it is impossible to do at standard temperatures and pressures like that at SATP. It has been done by the Z-Machine at the Sandia National Laboratories by using a pressure of 10 million times normal Atmospheric pressure. To create the pressure, the machine's magnetic fields hurled small plates at the diamond
    at 34 kilometers per second (21 miles per second), or faster than the Earth orbits the Sun.
    Unfortunately in open air, the fact that is it large network of covalently bonded carbons make it extremely hard to melt in the first place. Secondly, diamond at high temperatures will not melt, rather it will prefer to burn, as characteristic of all carbon allotropes. A diamond will burn or oxidize when exposed to a hot flame in the presence of oxygen, for example an oxygen torch with a temperature of 800 degrees C (1,472 degrees F), according to The Merck Index, a standard chemistry reference work.


    but it can be melted in the absence of air (or in vacuum) at a very very very high temperature
    A melted diamond is uncommon.
     
  11. Feb 22, 2014 #10
    Obviously objects that are solid at standard temperatures and pressures do not melt at standard temperatures generally.
    No, diamond cannot be melted in vacuum. Solid diamond at low pressures and high temperatures is converted to solid graphite without melting.
     
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