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How did we know or discover that hydrogen has 1 proton and 1 electron. I know the atomic structures throughout the history, but still remains my elementary level question how did we know that certain atom have an exact number of protons?

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Probably many important results are missing, but roughly history goes like this:

  1. In 1815/16 William Prout hypothesized (Prout's hypothesis), based on atomic weight measurements at the time, that all elements were made up of multiples of hydrogen atoms.
  2. In 1886 Eugen Goldstein discovered positively charged canal rays in gas discharge tubes. They consisted of various particles, with the lightest ones being protons.
  3. In 1911 Ernest Rutherford showed that the charge of atoms is concentrated in the nucleus.
  4. Antonius Johannes van den Broek hypothesized in 1911 that the (atomic) number of the elements corresponds to the charge of its nucleus.
  5. This was confirmed by Henry Moseley in 1913 using x-ray spectroscopy
  6. The discovery/naming of the proton is ascribed to experiments of Rutherford from 1917 where he shot alpha particles on nitrogen gas, which gave him hydrogen nuclei. He concluded that nitrogen must contain hydrogen nuclei.
  7. Discrepency in atomic weights were then explained by the discovery of isotopes/neutron starting from Francis William Aston (1919)
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