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Question about ionic compounds

  1. Apr 4, 2016 #1
    When ionic compounds melt, do their state change or they are chemically changed? Or both? Since the electrostatic forces are overcame?
     
  2. jcsd
  3. Apr 4, 2016 #2

    Borek

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    Staff: Mentor

    They don't change chemically.

    But you are perfectly right about being confused. Trick is, we are trying to classify changes as physical or chemical, when they are often somewhere in between. Nature doesn't care about our classification attempts and has its own ways.
     
  4. Apr 4, 2016 #3
    some features of ionic compounds;-
    As solids they are almost always insulating , but when melted/dissolved they become highly conductive , because the ions are mobilized.
    they keep their chemical composition and ionic character. For example,even in the vapor phase sodium chloride exists as diatomic "molecules".

    Electrostatic forces between particles are strongest when the charges are high,

    and if the distance between the nuclei of the ions is small - In such cases, they generally have very high melting and boiling points and low vapor pressure
    when the local structure and bonding of an ionic solid is disrupted sufficiently to melt it, there are still strong long-range electrostatic forces of attraction holding the liquid together and preventing ions boiling to form a gas phase

    even room temperature ionic liquids have low vapor pressures, and require substantially higher temperature to boil.

    for details see https://en.wikipedia.org/wiki/Ionic_compound#Melting_and_boiling_points
     
  5. Apr 5, 2016 #4

    DrDu

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    Science Advisor

    Just want to comment a little bit on this. On melting, hardly any bonding in an ionic solid is overcome. The density change on melting is rather minor, so that the separation of the ions also hardly change. The ionic bonds are not directed, so the exact position of the ions hardly matters.
     
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