ATOMIC THEORY
ATOMIC THEORY| Democritus | Matter is discontinuous. |
| John Dalton | Provided experimental evidence of the atom and concluded it was indivisible. |
| J. J. Thomson | Through the study of cathode rays, he discovered the electrons and concluded that the atom was divisible into a thin positively charged cloud with the negative electrons sprinkled throughout. Thomson's model is often called the Plum Pudding model. |
| Ernest Rutherford | Used radioactivity to test Thomson's model. Because a few of the alpha particles were deflected at 180 degrees, Rutherford developed the solar system model of the atom with a nucleus containing protons and neutrons and the electrons in orbits outside the nucleus. |
| Niels Bohr | Investigated the lines of the atomic spectrum of hydrogen and modified the solar system model so that electrons had "allowed orbits" and only certain allowable energies. He quantized the electron. |
| Quantum Mechanics | Electrons have definite allowed energies but no definite orbitals around the nucleus. Electrons are considered waves, not particles. |
"Anyone who is not shocked by quantum theory has not understood it" -- Neils Bohr
APPLET EXPERIMENT: Elemental Spectra
Names
Aristotle, Democritus, J. J. Thomson, Ernest Rutherford, Niels Bohr
Address questions to
Dr. Baker
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last updated January 5, 2006