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How much of the structure of an atom can be seen?

Well, it depends on what you mean by "seen"! Since nobody can actually see an atom with "naked eyes", then of course you cannot see the internal structure either. However there are all sorts of probes, and the original discovery of the nucleus was made by a rather clever experiment of Rutherford, where he sent helium nuclei passing through a thin foil of metal, and noticed that most of the nuclei passed straight through, but some bounced back, some almost going straight back the way the came. That indicated that most of atoms are empty space, but there is a small hard core in there, and you can calculate the size of it just by figuring out the fraction of your original nuclei that did not even notice it, and using the thickness of the foil. I believe this was done in the 1910's or 20's.

Arthur Smith

Well, there is also atomic force microscopy (AFM) and scanning tunneling microscopy (STM). These methods have been used to resolve the electronic force contours of surfaces and molecules adsorbed onto surfaces with resolution on the scale of atomic dimensions (i.e., you see "bumps" where the atoms are, and the bumps are atom-sized). Then there is angularly-resolved photoemission of electrons, which have been used to measure the angular distribution of electrons emitted from atoms, molecules, and clusters. This allows scientists to "observe" the shape of the electronic orbitals. In short, although there is no way to directly "see" an atom, there are literally hundreds of ways that scientists can probe the details of atomic and molecular structure. Such scientists are variously called spectroscopists, atomic/molecular physicists, and/or physical chemists (like me).


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