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Homework Help: Body Centred and Face Centred

  1. Sep 12, 2013 #1
    Why can't the atoms along the edge of a body centred and a face centred structures touch each other? Is it something to with the reasoning that somehow if they were made to touch each other then we would not be able to get the face centred and body centred structure?
  2. jcsd
  3. Sep 13, 2013 #2
    Anybody there??!
  4. Sep 13, 2013 #3


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    There is always a distance between atoms ... you can think of it as a repulsion between the outer most electron shells. The best they can do is to share some valence electrons via ionic, metallic, or molecular bonding.

    Here is a more comprehensive explanation:
    http://sciencequestionswithchris.wordpress.com/2013/04/16/do-atoms-ever-actually-touch-each-other/ [Broken]
    Last edited by a moderator: May 6, 2017
  5. Sep 13, 2013 #4
    You took the meaning a bit literally. Though even I am talking about the literal meaning but that is because its written there in the material I am reading from. I am posting an attachment. Please see it. Now, in the attachment, the atoms in the (a) part (simple cubic structure) touch each other along the edges but that is not the case in (b) and (c) (face centred cubic strucutre and body centred cubic structure). My question is why can't we make the atoms touch along the edge in (b) and (c) and still let (b) and (c) be fcc and bcc? Is it not possible to do so? Why or why not?

    Attached Files:

  6. Sep 13, 2013 #5
    My grasp on Solid state stuff isn't really good, the following might be wrong.

    Yes, it is not possible to do so. Do you see how a lattice is made? I hope you know that those blue, orange and red thingies (they have same radius) are part of atoms. Consider the fcc lattice, try to make the corner atoms (the red and orange) touch each other, do you think there would be enough space left to fit that face-centered blue atom? Simple geometry might help.
  7. Sep 13, 2013 #6


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    Those aren't atoms in the images; those are graphical representations to help visualize the different cubic structures. They are large so that you can see the "cuts" required to show how some of them are shared between the "unit cells". See here for other visualizations: http://en.wikipedia.org/wiki/Cubic_crystal_system

    See this article on two atom thick glass to see what atoms "look like" under a really good transmission electron microscope.
  8. Sep 13, 2013 #7
    Hmm..Even I thought the same thing..but wanted to confirm it. Does anyone else also say that? I'll go with the majority then. BTW are you preparing for IIT JEE?
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