| A | B |
|---|
| John Dalton | greatly expanded our understanding of the atom and elements; descibed atoms as tiny, hard spheres |
| J.J. Thompson | identified the electron; created the "plum pudding" (or chocolate chip) model |
| Ernest Rutherford | proved that most of the atom is empty space with electrons outside the nucleus |
| Niels Bohr | developed the first model of the atom; described electron movement as following a fixed path, or orbit |
| Erwin Schrodinger | described energy levels and the "electron cloud" |
| James Chadwick | identified the neutron |
| Dimitri Mendeleev | first to organize the elements into a periodic table; arranged them by atomic mass |
| Henry Moseley | rearranged the periodic table according to atomic number |
