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Determining the positive and negative poles of a molecule

  1. Sep 28, 2017 #1
    1. The problem statement, all variables and given/known data
    For the molecule CHCl3,

    a) Draw the electron dot diagram and structural formula
    b) predict the shape
    c) predict whether it is polar or non-polar, and justify your prediction. Indicate the positive and negative poles.

    2. Relevant equations

    3. The attempt at a solution

    Are there any websites or programs that will allow me to create lewis dot diagrams, structural formulas, and all of that fun stuff on a computer? As of right now I am doing it on paper and uploading it for my teacher.

    a) My electron dot diagram is correct, I searched it up online. The structural formula is Carbon as the central atom with Hydrogen above it, and three Cl atoms surrounding it. They are all single bonds.

    b) The shape of CHCl3 is tetrahedral because the central carbon atom is surrounded by 4 bonding pairs, and 0 lone pairs.

    c) This is probably incorrect but I gave it a shot.

    C = 2.5 EN
    H = 2.2 EN
    Cl = 3.1 EN

    The hydrogen dipole arrow is pointed in the direction of carbon because carbon is more electronegative than hydrogen. The chlorine bond dipole arrows point in the direction of chlorine because it is more electronegative than carbon and hydrogen. The dipoles are not identical in strength, they are not arranged symmetrically, and they do not cancel each other out therefore the molecule is polar.

    I'm not sure how to figure out which poles are positive and which are negative. Would Hydrogen be the negative pole, and Chlorine be the positive pole? Hydrogen is the least electronegative of the 3 atoms, and chlorine is the most electronegative of the 3. What would carbon be?

    Any help is appreciated, thanks!
  2. jcsd
  3. Sep 28, 2017 #2


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    Staff: Mentor

    Do you know geometry of the methane molecule?

    In general the most electronegative element draws most electrons to itself. What kind of charge - positive or negative - will it have?
  4. Sep 28, 2017 #3
    By geometry, do you mean molecular shape? I just learned that in this lesson. VSEPR says that methane would be a tetrahedral shape.

    If the most electronegative element draws electrons to itself (chlorine in my question) wouldn't it have a positive charge? I'm still confused by this.
  5. Sep 28, 2017 #4


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    Staff: Mentor

    Right. If three hydrogen atoms are replaced they have to on one side of the carbon - so we can expect the molecule to have a a dipole moment.

    It draws electrons, so it has an excess of electrons. What is the electron charge?
  6. Sep 28, 2017 #5
    Ahh okay. So the chlorine side would be negative and the hydrogen side would be positive.
  7. Sep 28, 2017 #6


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    Staff: Mentor

  8. Sep 28, 2017 #7
    Thanks for the help!
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