How do you model an atom?
These sites may help you.
http://education.jlab.org/qa/atom_model.html
http://www.windows.ucar.edu/tour/link=/physical_science/physics/atom_particle/atom.html
http://education.jlab.org/qa/atom_model.html
http://www.windows.ucar.edu/tour/link=/physical_science/physics/atom_particle/atom.html