Help with math...

Discussion in 'General Discussion' started by GreenCream, Mar 11, 2011.

  1. GreenCream

    GreenCream Well-Known Member

    May 25, 2010
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    Hi, I'm really stuck on an extra credit math problem my teacher gave me. When all of the points on a methane molecule are connected, they form a tetrahedron, right? Well, I have to find the angle formed by the carbon and 2 hydrogens. I know that I could look up the answer online, but I need to show work.

    It involves nothing higher than trigonometry.

    Help, please?
  2. tikgnat

    tikgnat Baweepgranaweepninnybong. TFW2005 Supporter

    Jul 2, 2002
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    Beneath the Loft, London, UK
    This question needs a diagram. Even the chemical formula CH4 would have been useful.

    I had to go to google, to find what layout a methane molecule has just to visualise the question!

    Anyway, I worked it out, its a piece of cake.

    It's not even trignometry, all you have to understand is its to do with equilateral triangles, forming a right angle triangle within that equilateral triangle, and remember that all internal angles in a triangle add up to 180.

    Having said that, I worked it out on a 2D plane, I'm not sure if the angles vary slightly when changed to a 3D plane. I don't think they do though.
    Last edited: Mar 11, 2011
  3. Aernaroth

    Aernaroth <b><font color=blue>I voted for Super_Megatron and Veteran

    Mar 27, 2004
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    This is called a lewis structure. You can google that if you'd like. Figure out how many bonds are in the molecule, and then figure out how many electron pairs are in the structure (none, in this case).

    When a molecule forms, bonded atoms want to be as far away from eachother as possible. So on a single plane (looking at the molecule from the top, side, bottom, front, back, etc.) you'll see three atoms (and then one moving in or out of the page). So they want to be as spaced out as possible, and they have 360 degrees to do so. 360/3 is 120 degrees between each atom. No matter what face you look at the molecule from, there will be 120 degrees between each hydrogen atom with the carbon at the centre.

    Google up a picture of a methane atom and you'll see what I mean.

    But now that I've done your homework for you, you have to do a bonus question for us. Same idea, what's the angle between two atoms. But in this case I want you to find us the angle created by a line of three carbon atoms in graphite and diamond. Graphite is an allotrope of carbon where the carbon bonds in two-dimensional hexagonal sheets, and carbon forms 3 dimensional structures in diamond where each carbon atom is bonded to 6 other carbon atoms. Go go go!

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