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Basic chemistry: sulphur dioxide shape?

  1. Jan 4, 2012 #1
    Basic chemistry: sulphur dioxide shape??!

    I realize this isn't homework, but it's so basic I'm ashamed of putting it in the chemistry section. I'm trying to self-teach here, but my textbook is awful and I'm even worse.

    Question: Workout the shape of SO2.

    Step 1: Draw lewis diagram to work out how lone pairs and bonds are arranged. That's my first problem. I can't figure out how in high heaven the funny dots fits together in a way that works. Resigned, I improvise step 2

    Step 2: Go onto wikipedia and discover that SO2 is structured O=S=O. Problem #2. Since when did sulphur get 10 electrons in the valence shell?? Ignoring the lone pair apparently in limbo I finish the question.

    Step 3: 2 double bonds → 2 electron clouds → a linear molecule.
    Checking the answers, SO2 is bent. Apparently, I should have counted the 5th pair. :grumpy:


    So ultimately my question is: why does sulphur has 10 electrons in SO2? Very confused here and any help will be appreciated. Thanks in advance.
     
  2. jcsd
  3. Jan 4, 2012 #2
    Re: Basic chemistry: sulphur dioxide shape??!

    Sulphur has 6 valence electrons. The bond formed is O-S-O where the angle OSO is 120 degree.
    In this structure, sulphure shares a pair of electrons with oxygen. This bond is partially double bond. The bond length is 143 pm which comes between single and double bond length(due to resonance)
    The concept is bit too high.
    Simply see it as, sulphur has 1 lone pairs in this bond.
     
  4. Jan 4, 2012 #3
    Re: Basic chemistry: sulphur dioxide shape??!

    Still trying to get my head round this... I don't get the 'partially double bond' bit. Isn't sharing a pair of electrons by definition a single bond???
    Thanks for the reply.
     
  5. Jan 5, 2012 #4
    Re: Basic chemistry: sulphur dioxide shape??!

    Partial double means that the double bond can shift between the two oxygen molecules.
    Resonance[/PLAIN] [Broken]
     
    Last edited by a moderator: May 5, 2017
  6. Jan 5, 2012 #5

    Borek

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    Staff: Mentor

    Re: Basic chemistry: sulphur dioxide shape??!

    You might want to correct it.
     
  7. Jan 5, 2012 #6
    Re: Basic chemistry: sulphur dioxide shape??!

    Oh...
    That seems... unfair. Why does chemistry have to be more complicated than it already is???
    Thanks for the help anyway guys, this is probably a bit beyond what I'm supposed to learn but it's good to know how the molecule works. :frown:
     
  8. Jan 5, 2012 #7
    Re: Basic chemistry: sulphur dioxide shape??!

    Sorry, Borek.
    IT shifts between one oxygen molecule and sulphur molecule pair to the other oxygen and sulphur molecule pair where sulphur is common to both.
     
    Last edited: Jan 5, 2012
  9. Jan 6, 2012 #8

    Borek

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    Staff: Mentor

    Re: Basic chemistry: sulphur dioxide shape??!

    I understand English is not your first language? Please check exact meaning of the words molecule, atom and bond - what you wrote makes no sense. Oxygen molecule is O2. I guess you mean electrons move between oxygen-sulfur bonds inside the SO2 molecule.
     
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