text: The idea of some particle having a negative charge was needed to properly explain the results of experiments performed by scientists like Thompson, Rutherford, and Bohr.  Keep in mind that no one has actually seen an electron, but it is part of the atomic theory, and it is an idea that has been proven by experimentation.  More information on atomic theory can be found here:\n http://www.scienceclarified.com/As-Bi/Atomic-Theory.html\n\nHere is another link to a paper called "The Nature of Electronic Charge."  It's pretty theoretical, but perhaps it will be of use to you.\nhttp://arxiv.org/ftp/physics/papers/0408/0408053.pdf