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Lewis Structure + Molecular shapes

  1. Apr 13, 2005 #1
    3. Which of the following is the molecular shape of the ion, ICl4-?

    A. Tetrahedral
    B. See saw
    C. Square planar
    D. Square pyramidal
    E. Trigonal pyramidal

    I drew the lewis structure, 4 chlorines bound to an Iodine. Iodine has 7, Each clorine has 7 with 35 total, the bonds account for 4, so distributing the rest of the 31 electrons, I put 6 on each chloride, and 6 on the iodine, with the extra electron floating since its a negative ion.

    This is kinda bugging me since Iodine has 8 electrons from the bonds alone, and now the extra electrons put it up to 14. I must have drawn it wrong, but anyway:

    Molecular shape is decided by electron domains, and since we have 4 from bonds and 3 from electron pairs, 7 total. Thats way too many, we only went up to 6 electron domains in class, and thats for a square planar.

    Help? My test is next week.
     
  2. jcsd
  3. Apr 14, 2005 #2

    dextercioby

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    It can't be square planar.It's a square pyramid.I hope u see why.


    Daniel.
     
  4. Apr 14, 2005 #3
    In all honesty I cant relate the names to the geometries.

    I know the seesaw one is a vertical (z) axis, and on the xy plane, 3 branches 120 degrees apart.

    I believe square planar is shaped like an x,y,z axis is set up.

    Do you know if I did my lewis structure right?
     
  5. Apr 14, 2005 #4
    Also the answer sheet says its square planar.
     
  6. Apr 14, 2005 #5

    dextercioby

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    Yes,one electron does provide the mesomerical (Pauling) structures...But it's okay.Just the geometry that u found was incorrect.Maybe u'll learn about Gillespie's models,too.

    Daniel.
     
  7. Apr 14, 2005 #6
    I have no idea of what what you jsut said means.
     
  8. Apr 14, 2005 #7

    dextercioby

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    I'm sorry,you're right.The hybridization is not [itex] \mbox{sp}^{3} [/itex],so it's not a pyramid (somewhat similar to methane).The "d" orbitals of Iodine participate,too.I think it's [itex] \text{sp}^{2}\text{d} [/itex] who's got a planar structure.


    Daniel.
     
  9. Apr 14, 2005 #8

    Gokul43201

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    The hybridization is [itex]sp^3d^2[/itex]. The structure is square planar. There will be two non-bonding pairs oriented normal to the plane (along +z and -z).
     
  10. Apr 14, 2005 #9

    Gokul43201

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    Here's your mistake. There are only 6 pairs : 4 bonding pairs with the chlorines, (that leaves 3 electrons on I, plus the extra electron for the negative charge), and 2 non-bonding pairs.
     
  11. Apr 14, 2005 #10

    dextercioby

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    That means two things

    1.I screwed it up real badly. :frown:
    2.The structure should be octaedrical.But it's square planar,because of the 2 nonbonding pairs which don't count.Reminds me of water molecule with 2 non bonding pairs.

    Daniel.
     
  12. Apr 14, 2005 #11
    Ok so there are two electron pair domains on the iodine aside from the bonds. So the chlorines iwll all be one a plane. The extra electron pairs will go perpendicular to this plane, and since they arent molecular, have no structure.

    The electron geometry would be the x-y-z looking one, octahedral?
     
  13. Apr 14, 2005 #12

    dextercioby

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    Yes,it should be octaedrical,typical for [itex] \mbox{sp}^{3}\mbox{d}^{2} [/itex] hybridization.

    Daniel.
     
  14. Apr 14, 2005 #13

    Gokul43201

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    I'm not sure if this is what you mean by "x-y-z looking one" but essentially, you have one electron pair pointing along each of the 6 rectangular co-ordinate axes directions (+x, -x, +y, -y, +z, -z). The alternate way of picturing it is in terms of a pair of square pyramids stuck to each other; or otherwise, 4 pairs pointing towards the corners of a square (with the central atom in the middle of the square) and 2 pairs pointing normally up and down.
     
  15. Apr 14, 2005 #14
    xyz looking one means the structure where it lokos like the xyz axes on a graph. I believe we are talking about the same one, octahedral. I just need to look over the names of the geometries.

    Thanks to both of you.
     
  16. Apr 15, 2005 #15
    It would be [c] because looking at I itself, it has 2 lone pair (4 valence electrons; don't forget the -ve charge on the molecule) and 4 arms sticking out to hold the Cl atoms to it.

    Don't panic, try to visualise it this way....a piece of square cardboard with the I atom in the middle, 4 Cl atoms at the corners, and then you have 2 big lobes (2 lone paris) sticking out from the top and bottom of the cardboard.

    Hope this helps! :smile:
     
  17. Apr 15, 2005 #16
    Some additional notes to help you prepare (try to memorise them!)

    Bonding domains (BD) - bonded to another atom
    Non-bonding domains (NBD) - signify lone pairs

    [2 pairs]
    Linear - 2 BD, 0 NBD e.g. CO2

    [3 pairs] incld lone pairs
    Trigonal planar - 3 BD, 0 NBD
    Bent - 2 BD, 1 NBD

    [4 pairs] incld lone pairs
    Tetrahedral - 4 BD, 0 NBD
    Trigonal pyramidal - 3 BD, 1 NBD
    Bent (tetrahedral) - 2 BD, 2 NBD e.g. H20

    [5 pairs] incld lone pairs
    Trigonal bipyrimidal - 5 BD, 0 NBD
    Seesaw - 4 BD, 1 NBD
    T-shaped - 3 BD, 2 NBD
    Linear (trigonal bipyramidal) - 2 BD, 3 NBD *this one has 3 lobes (3 lone pairs) surrounding the central atom on a plane and 2 atom attached to it from the top and bottom.*

    [6 pairs] incld lone pairs
    Octahedral - 6 BD, 0 NBD
    Square pyrimidal - 5 BD, 1 NBD
    Square planar - 4 BD, 2 NBD
     
  18. Apr 15, 2005 #17

    dextercioby

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    Hold on a second.Isn't [itex] \mbox{CO}_{2} [/itex]

    [tex] \left|\bar{O}=C=\bar{O}\right| [/tex]

    ,with 4 pairs ...?


    Daniel.
     
  19. Apr 15, 2005 #18
    CO2 has 2 bonding domains, the lone pairs are on the oxygen atoms and not the central carbon atom. Each double bond counts as one electron domain.

    No of electron domains = No of atoms bonded to central atom + No of non-bonding pairs on the central atom.
     
  20. Apr 15, 2005 #19

    dextercioby

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    Okay,i see.I wasn't familiar with this terminology.

    Daniel.
     
  21. Apr 29, 2008 #20
    where does the extra electron come from that makes the entire molecule negative?
     
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