A question for chemists

Discussion in 'Chemistry' started by pluto2, Jun 16, 2009.

  1. pluto2 Registered Senior Member

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    773
    A question for chemists...

    How do you know how a substance looks like or feels like in real life from a drawing of it's chemical structure alone? And more importantly how do you know it vice versa, the chemical composition of a substance from how it looks and feels like in real life?

    For example, trifluoroacetic acid, how do I know what it looks like in real life from a chemical structure drawing like this?

    Also how were the chemical elements first discovered without the aid of powerful microscopes?
     
    Last edited: Jun 16, 2009
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  3. Smartteaser192 Registered Member

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    I actually had the same question few weeks ago. A teacher of mine told me that they use imagination. As Einstein said:

    “Imagination is more important than knowledge. For knowledge is limited to all we now know and understand, while imagination embraces the entire world, and all there ever will be to know and understand.”

    So, that's the connection.
     
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  5. Trippy ALEA IACTA EST Staff Member

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    The short answer is you don't really, but there are certain 'rules' (they're more like guidelines really) that we can use to guess.

    The long answer is slightly more complicated, consider your example, Trifluoroacetic Acid. Based on it's structure I would guess that it's probably a clear liquid (which might be oily) at room temperature, the logic being that it's highly polar, and capable of hydrogen bonding, which should also make it water soluble, and this would tend to be confirmed by Vinegar. I predict that it's clear and colourless on the basis that there is no conjugated system of double bonds (which is one of the requirements for colour), and I would expect it to be a lot more acidic then acetic acid (because C-F bonds are strongly polar, and effectively electron density is drawn through the σ-bond network weakening the O-H bond, the strength of which determines acidity (weak bond = easier to remove the H = stronger acid).

    It's equal parts experience and knowledge really.

    On the other hand, if you were to give me a sample of a white crystalline solid, or a clear oily liquid i'm probably not going to be able to tell you much about it without performing some kind of test, for example, without tests there's no real way of distinguishing between table salt and sugar (remember, tasting is still a test, but if I hand you an anonymous white crystalline powder, it's not neccessarily safe to taste it, It could be table salt, it could be sugar, but it could just as easily be MDMA or Sodium Cyanide).
     
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  7. Dywyddyr Penguinaciously duckalicious. Valued Senior Member

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    Imagination won't let you know.

    To reinforce Trippy's point I once asked a similar question and got the answer - "That's why chemistry is an experimental science!".
    You do the experiment - i.e. make the stuff, and then look at it.
     
  8. Billy T Use Sugar Cane Alcohol car Fuel Valued Senior Member

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    I am not a chemist, but interested in processes used to discover /invent new medical drugs. Many are proteins or simuliar structures of a huge number of atoms. Often first studies are in computer 3D models to see how they will / may fold up. The 3D shape may fit with some specific binding site of a cell and if it does so, and is a stable compound, it may be biologically useful. Often what atoms make it up is not as important as the 3D shape they take.

    Modern computer models have gotten to be pretty good at predicting that.
     
  9. I'm not a chemist either, but my guess would be that the letters in the picture mean certain things (probably elements)
     

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