• Question: What evidence was used to support the atomic theory?

    Asked by rhooper821 to Ben, Dave, Ed, Sam, Susana on 19 Jun 2013.
    • Photo: David Briggs

      David Briggs answered on 19 Jun 2013:

      I think it was a chap called Ernst Rutherford (working here in Manchester) who nailed the model of a tiny nucleus surrounded by orbiting electrons – he did an experiments where he bombarded gold foil with alpha radiation – the models of the time suggested that the alpha radiation should all pass straight through – but he found some of it bounced back – suggesting that there is a core or nucleus to the atom that was causing some of the alpha radiation to bounce.

      He was a really great scientist, and won the Nobel prize.

    • Photo: Sam Horrell

      Sam Horrell answered on 19 Jun 2013:

      X-ray crystallography is a great source of evidence for the atomic theory, probably wasn’t used originally but it’s still pretty cool. Because the wavelength of an X-ray is similar in length to the distance between an atomic bond X-rays are scattered by the electrons srurrounding the atoms. This is just like when visible light scatters off things and your eyes focus the light to form an image. We focus the X-rays that scatter off the electrons using a computer and they allows us to see a protein’s atomic structure. It’s effectively X-ray vision.

    • Photo: Ed Lowe

      Ed Lowe answered on 19 Jun 2013:

      Another piece of evidence for the atomic theory of matter (rather earlier and more indirect) was when John Dalton used the concept of atoms to explain why different elements always reacted in whole number ratios – this was back in the early 19th century when he had no means of directly observing anything on an atomic scale.

      The atomic theory was well established before these next two techniques came along, but both electron microscopy and atomic force microscopy can allow scientists to look directly at atoms. Those of us working in biology tend to think of them as lower resolution techniques since they can’t see individual atoms of light elements like carbon, oxygen and nitrogen but there are some beautiful images of arrays of gold atoms (for example).

    • Photo: Susana Teixeira

      Susana Teixeira answered on 21 Jun 2013:

      A bunch! Nowadays there are techniques that allow you to “see” atoms directly, as Ed mentioned, but ~400B.C. Democritus suggested that all matter was made of atoms based on no evidence.
      Much later Dalton said atoms would explain the behaviour and proportions in mixtures of gases for example. Thomson was studying cathode rays and found electrons, while Rutherford realised the atom had a nucleus, with protons inside, because of experiments where he shot particles against a thin gold foil (not all went through!). Bohr suggested energy levels for electrons from experiments with hydrogen. Chadwick, a student of Rutherford’s, discovered neutrons (that I use everyday!) when bombarding a heavy element with alpha particles (helium nuclei).
      So the model has been building up and it is now even more sophisticated with the help of Schrodinger and Heisenberg. We will probably keep adding detail to it even more!

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