The answer depends a bit on what you mean by "what actually particles look like ". What individual atoms or small molecules actually look like is of course nothing since they’re too small to see with visible light. However, the sorts of descriptions people make with patterns of atomic positions and patterns of electronic states around the atoms or in molecules have very strong support, some of which can easily be pictured.
One of the nicest pictures of both atoms and electronic states comes from the work of Don Eigler and coworkers at IBM using a scanning tunneling microscope to look at surface atoms. The STM gives a signal sensitive to how easily electrons move from its tip to the surface, and that signal can be plotted vs. position of the tip to make a nice picture. Each surface atom can be directly detected by the STM. Furthermore, inside a ring of surface atoms, those mysterious quantum states of the electrons actually produce a clearly detectable pattern, like waves on a drum. To get a truly spectacular set of images, go to http://www.google.com
, select the images search, and search for the words "quantum corral".
For other arrangements of atoms- say in an NaCl crystal- the ’seeing’ is done different ways. Often, the pattern of scattering of x-rays or neutrons gives an unambiguous picture of how the atoms are arranged. Other techniques used to measure how electrons are arranged in atoms, molecules, and crystals include several light-scattering and spin resonance methods.
You ask if the talk is ’all theory’. Sometimes the word ’theory’ is used to mean ’guess’ or ’vague speculation’. In this case the theory, quantum mechanics, is not vague and is supported by an enormous array of precise measurements. It tells us the mathematical form of the electronic states in small molecules, etc. However, any attempt to draw pictures of those states always distorts the content of the mathematical description. Sometimes the bond pictures used in chemistry are good approximations, but sometimes the electronic states don’t lend themselves to that simplification.
(republished on 07/21/06)