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Picture of a real atom?

  1. Nov 29, 2006 #1
    I think I heard from a Nobel Laurete in Physics that from the Electron microscope we were able to see the picture of a real atom for the first time in the 70s. But my chemistry textbook written in 2000 said that no one has actually seen an atom. What is going on?
    Last edited: Nov 29, 2006
  2. jcsd
  3. Nov 29, 2006 #2


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    I guess it depends on what it means "to see".
  4. Nov 29, 2006 #3
    That depends on what you mean by 'see'. No one has every seen a single atom with an optical microscope. But there are pictures using Atomic Force Microscopes (AFM) that clearly show topological 'pits' where atoms lay. I believe Scanning-tunnelling microscopes (STMs) also are stong enough to depict single atoms, but I'm no 100% sure.

    Brief summary on AFM http://images.google.ca/imgres?imgu...images?q=afm+pictures&svnum=10&hl=en&lr=&sa=G

    Pictures of atoms taken by AFM http://images.google.ca/imgres?imgu...afm+&start=18&ndsp=18&svnum=10&hl=en&lr=&sa=N
  5. Nov 29, 2006 #4
  6. Nov 29, 2006 #5
  7. Nov 29, 2006 #6

    Your guess is as good as mine, the picture should be labelled better. I'm guessing that each 'sphere' is an atom and that we are looking at some kind of crystalline structure, perhaps a metal, or a quartz or something with a well ordered atomic structure. I can say for sure that we are not looking at quarks or electrons (because they have never been observed as having a 'real' geometric structure), I'm not so sure about protons or neturons.

    If you are really interested, e-mail the website master and I'm sure they'd help you out since its an academic institute.
  8. Nov 29, 2006 #7
    The experimental techniques you are referring to show the interaction of the apparatus with the specimen that you study. So the plots show how this interaction varies as you probe/scan the specimen. For example, changes in colour or intensity indicate a region where there are certain atoms. The theory behind the interaction will completely tell you which regions correspond to what kind of atoms.

    But, you DO NOT observe individual atoms at there socalled exact location on the specim. This would directly violate the Uncertainty principle.

    Concerning the quarks that are mentioned in a following post here. NO, you cannot observe the internal structure of quarks, or quarks themselves (as socalled point particles or whatever) because they are elementary particles that, like all phenomena in "the quantum world" respect the HUP. Elementary particles are the most fundamental building blocks of the theoretical models that describe interactions between all kinds of atoms.

  9. Nov 29, 2006 #8
    I remember reading about techniques that claimed to "see" the shapes of electron orbitals, which is most likely being referred to here, i.e., the structure of the atom, rather than the structure of the nucleus (protons and neutrons), nor the structure of the nucleons (quarks).

    I won't do the calculation right now, but surely.. evidently.. you can measure an atom's location (ie. within about an angstrom) without violating the uncertainty principle (presuming it's not at absolute zero temperature)?
  10. Nov 29, 2006 #9
    This would mean there is a bit of uncertainty in everything we measure (even if there is no experimental error) which sounds very plausible. I always believed in the idea that everything we do is varying degrees of approximations to something. Although I do not know what that something is because even these sentences is an approximation to something.:confused:

    So we can't see quarks because they are elementary particles. Could you say a bit more? It seems like a surface explanation. Is it because the HUP would suggest that if we were able to see it, it would look too fuzzy for us to notice and probably couldn't recognise it. The quark's momentum would be too great?
  11. Nov 29, 2006 #10

    I didn't know HUP applies to observing atoms. Is this because the atoms have a momentum, even if ever so slight, like a thermal jittering?

    I found this explanation of how a Scanning-Tunnelling Microscope works and the uncertainty of the atoms's position and in this case, is due to the probabilistic decay of the tunneling current with respect to its distance from each atom: http://images.google.ca/imgres?imgu...bnw=137&prev=/images?q=stm&svnum=10&hl=en&lr=

    Also, here is a link to several STM pictures that clearly show various arrangements of atoms, I realize the 'peaks', which represent single atoms, are probabilistic guidlines to the 'area' where each atom is and in no way are 100% certainties of each atom's location: http://images.google.ca/imgres?imgu...bnw=137&prev=/images?q=stm&svnum=10&hl=en&lr=

    More: http://images.google.ca/imgres?imgu...bnw=137&prev=/images?q=stm&svnum=10&hl=en&lr=
  12. Nov 30, 2006 #11

    To me the shape kind of looks like a probability distribution for an electron shell. So I guess it is possible that the structure visible on these atoms is actually the outermost electron shell... here is some nice picture for comparison: http://www2.wwnorton.com/college/chemistry/chemconnections/Stars/images/orbitals.jpg
  13. Nov 30, 2006 #12


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  14. Dec 2, 2006 #13
    The HUP applies to every physical entity that is described by QM. The HUP is a fundamental property of the QM formalism. Indeed, the momentum is an important factor here but what the exact value is is irrelevant. Whatis for sure is that there will be a spread in momentum (p) if you would measure it. Just to be clear : suppose you have a device that measures p with a 100 % of accuracy. So, you get a nice number for p with no error margin. This is very possible and does NOT violate the HUP. The HUP states that if you would measure 100 atoms with that device ("at the same location") and if you then plot the p-values, you will get a spread in p-values.

    My point : the HUP has NOTHING to do with the devices that you use and their accuracy but has EVERYTHING to do with the QM formalism and the particle/wave "duality". In classical physics, the concept of diffraction (waves !!!) exhibits the exact same properties as those of the HUP. "If you make the hole smaller, the spread of the wave passing through it will be bigger"

    The distance to each atom that you talk about is not the actual distance from the probe to that atom. this would again violate the HUP since you cannot know the exact location of that atom. This distance varies because the potential value is set to remain constant. Again, what is plotted is the interaction (ie the QM tunneling-effect)between the probe and the specimen.

    I urge you to study this plot (quantum coral) more carefully. I mean, try to figure out what had been plotted exactly. You do NOT just see some region where there is a certain probability of seeing an atom or electron...

  15. Dec 2, 2006 #14
    You cannot just see (ie observe their cartesian coordinates or something like that) orbitals because they are a mathematical abstraction resulting from the QM formalism. What you SEE is the INTERACTION (change in V during tunneling while the distance is kept constant for example) between probe and material. Besides, orbitals are not entirely described by spatial coordinates. Why do you think the orbitals are determined by quantum numbers like the l or m quantumnumber.

    I don't get is this : you say that you can see (meaning acquire the spatial coordinates) electron orbitals to study the structure of atoms. But this does not work for protons and neutrons. But since those particles make up the nucleus, how can you then study an entire atom properly ?

    Well, let me tell you this : If technology would allow it, you could measure the position of an atom, electron, etc etc with 100% accuracy. This does NOT violate the HUP. What do you think about that ?

    So my point is, what you state above is something i never tried to argue here.

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