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Why is mercury a liquid even though its atoms are closely packed

  1. Jun 15, 2008 #1
    the density of ice(solid) is less than that of water(liquid) and density of mercury(liquid) is more than that of many solids.
    thinking about it, it seemed natural to me that the more closely are the atoms or molecules packed the greater will be their density. but on packing them closely, isnt the state also going to be more solid-like?
    so what determines a substances density and what determines its state?
    what keeps the H20 molecules in place in ice but not as tightly packed as in liquid water so that its density is reduced? and why is mercury a liquid even though its atoms are (obviously?) closely packed?
     
  2. jcsd
  3. Jun 15, 2008 #2

    mgb_phys

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    Water is anomolous in it's solid state being less dense than liquid.
    It depends on the crystal structure which depends on the bond angle and chemical nature of the bonds.

    Mercury is a liquid because it's outer electrons are very strongly bonded.
    Strongly attatched outer electrons aren't free to bond with other atoms and so the metal is softer because it takes less energy to break the bonds. Mercury is the ultimate example of this.
    Gold has a half full outer shell and so also has relatively weak bonds to other atoms and is a soft metal.
     
    Last edited: Jun 15, 2008
  4. Jun 16, 2008 #3
    Ya, as was mentioned, water ice is an anomaly and the reason is because it forms a hexagonal lattice structure like the one shown here:

    http://www.cs.cmu.edu/~dst/ATG/images/ice1h.gif

    Therefore, if you look at the lattice structure you'll see that there is a lot of open space and thus it has a lower density. However, it is not the general case that a molecule will form such an open spacious lattice
     
  5. Jun 16, 2008 #4
    thanks mgb_phys and maverick_starstrider. i understand that water-ice is an anomaly.

    What are the outer electrons in mercury strongly bonded to? Do you mean that outer electrons(valence electrons right?) are not easily available to participate in reactions? In mercury, which is a metal, the outer electrons are 'free' in a sense to conduct electricity right?

    Is that also why all the 'stable' elements like He, Ne, Ar etc are gases?
     
  6. Jun 17, 2008 #5

    mgb_phys

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    The outer electrons - like all the others are strongly attracted to the nucleus, in mercury the large mass and charge of the nucleus mean the outer valence electrons are very strongly held - so aren't available to do the nomal free electron sea metal thing. (although they must have some freedom or mercury wouldn't be shiny!)

    http://antoine.frostburg.edu/chem/senese/101/periodic/faq/why-is-mercury-liquid.shtml

    The noble gases are gases because theie outer shells are completely full and so there are no free electrons to bond with other atoms of the same species. If the atoms are all on their own they are pretty much forced to be a gas. Interestingly mercury gas is single atoms like a noble gas.
     
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