• Question: How do scientists know they are such things as atoms?

    Asked by rachel14 to Cathal, Ciara, Emma, Michael, Sive on 13 Nov 2013.
    • Photo: Cathal Cummins

      Cathal Cummins answered on 13 Nov 2013:

      Good question Rachel. A hundred years ago, we couldn’t know with certainty that atoms existed, however nowadays we have a “camera” that actually allows us to take a picture of an atom! Check it out, it’s called a scanning tunnel microscope (STM). It’s basically a _really_ sharp pin that can trace the shape of the atom using electricity. There are plenty of other pieces of evidence but I think this is something that, when you see it, you’ll be convinced that atoms do indeed exist! 🙂

    • Photo: Michael Nolan

      Michael Nolan answered on 13 Nov 2013:

      Hi Rachel,

      Always a good question…

      We can now see atoms, say on the surface of a metal crystal, using microscopes that use electrons instead of light to see objects. The microscope works on the ideas that the size of an object that is visible depends on the wavelength of what you view it with. The wavelength of light allows us to see around 1 millionth of a metre.

      The microscopes now used to view atoms use electrons which allows you to see objects the size of atoms. These are called STM, SEM or TEM (scanning tunneling, scanning electron and transmission electron) microscopes.
      So with these microscope we can see for the first time atoms and even follow chemistry on a surface.

      Outside of this, atoms were hypothesised to explain how gases behave in a container and then the likes of Dalton proposed that every element is made up of small, indivisible particles (atoms) but they are so small you cannot see them. Einstein worked on Brownian motion (random movement of seeds in water) and used the atomic idea to explain it. A number of key experiments between 1900 and 1926 could only be explained by atoms. So until we could actually see atoms with the newest microscopes, we had to rely on their existence being the only way to explain multiple phenomena.
      This idea is usually very powerful.

      We recently worked with a team in Paris to show different types of iron atoms in an iron-titanium structure and the microscopes there could image iron in different states, atom-by-atom!

      some images
      researcher.ibm.com/researcher/view_project.php?id=4245
      http://www.princeton.edu/~kahnlab/STMImages.html‎

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