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How were atomic masses determined before mass spectroscopy existed?

  1. Dec 10, 2013 #1
    I remember a professor mentioning something about how scientists did this when we were discussing the history of the periodic table (they originally ordered it by atomic mass). I can't seem to find an answer online without digging through a lot of stuff...there was one article on this topic specifically but the link is dead.
     
  2. jcsd
  3. Dec 10, 2013 #2
    Beginning of this will give you an summary
    http://library.thinkquest.org/C006439/atomic/index.htm

    Bascically it was done by a lot and a lot of chemical reactions to fill in the spots -weighing reactants and products, measuring volumes.

    For example, water can be broken down into its constituents, hydrogen and oxygen in gaseous phase. So weigh the products and measure the volumes, use Avogadro, and other rules, and compare the results to get a ratio. Do more experiments to get more ratios and pick one of the elements as a standard which was oxygen in the beginning on which all others were based. Note that for one reaction, such as water, one would have to consider if the products were actually H and O, H2 and O, h and O2, etc. Other experiments would lead to a consensus.
     
  4. Dec 10, 2013 #3

    sophiecentaur

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    It is easy to forget just how hard they used to work at measuring things when they couldn't go down the road and buy a gizmo to do it. No wonder they got the initial stab at a periodic table wrong, when isotopes were messing with their measurements. A truly fantastic story, involving hundreds and hundreds of measurements, to reduce the errors.

    The same approach gave them a highly accurate model of the Solar System, long before there were massive telescopes or satellites.
     
  5. Dec 10, 2013 #4

    sophiecentaur

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    If you are not prepared to do this at times, you will not get far in Science, young man!
     
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