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How do we know the atomic number of an element?

  1. Nov 6, 2012 #1
    Here's what I know: Scientists used mass spectrometry to figure out the number of electrons in a neutral atom of the element. We know that if an atom has a neutral charge, the number of protons = the number of electrons - therefore, the atomic number = the number of electrons.

    Would anyone care to explain the process?
  2. jcsd
  3. Nov 7, 2012 #2


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    Interesting historical question which others may answer better. Perhaps here http://en.wikipedia.org/wiki/History_of_mass_spectrometry will help.

    This discovery of isotopes must surely have been a revelation, and a resolution of a suspicion or conundrum at the time, yet somehow it does not come over in handed-down historical legend or scientists' folklore or pantheons as one of the more shattering discoveries of the 20th century. I wonder if there is a history book that does justice to how it was seen in its time?
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