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Thread: Basic chemistry

  1. #1 Basic chemistry 
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    I am looking for a deeper understanding of bonding structures and I'm wondering someone knows the answer to this.

    When Na+ and Cl- come together, they form NaCl. As well all know, Cl has seven valence electrons while Na has one, so Cl forms an ionic bond with Na. What I don't understand is why each ion surrounds itself with six ions of opposite charge as opposed to any other number. Why not four or eight?

    The answer I got while searching on line is this:

    Ions with unlike charges attract each other, the chlorine ions will attract the sodium ions; but will hold off the other chlorine ions since ions with like charges repel each other. As a result of the attraction between the oppositely charged particles, each chlorine ion will surround itself with six sodium ions; each sodium ion will surround itself with six chlorine ions.

    To me, that second sentence is very poor. It doesn't at all describe why SIX ions surround the other one of opposite charge. Can someone illuminate this please?

    Thanks,

    MM


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  3. #2  
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    I think it's because sodium and chloride form a cubic close packing when they are ions. There are other packings, but I think this packing results in the 'lowest energy' possible.

    http://www.tg.rim.or.jp/~kanai/chemistry/cry3d-e.htm


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  4. #3  
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    We're talking about extremely close distances competing with charges. In three dimmenional space the closest you can have something to a central object while still being far away is each directly on the + and - sides of the x,y,z axis. After that, there's nowhere to go because of repulsion. Similar themes are common when studying bonding geometry, but I must admit I haven't reviewed Na+ and Cl- bonding, though both are 2nd period atoms and so relatively small.
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