<p> From thoughts about atoms to the nuclear model Aristotle: philosopher, hyle, matter has a continuous force inside it, did not believe in atoms Democritus: Greek philosopher, thought about atomos, invisible and indivisible Lavoisier: law of conservation of mass, combustion, and oxygen Proust: law of definite composition H2O everytime, not HO and H4O sometimes Dalton: first atomic theory, all matter is composed of indivisible atoms Davy: said that the color of an atom was dependent on the atom itself. He felt that it was caused by something in the atom. Used cathode rays and electricity, discovered Na, K, Mg, Ca, Sr, and Ba JJ Thompson: used cathode rays and the effect of a magnetic field to determine the mass and existence of a negative particle, discovered the electron, plum pudding model Millikan: performed the Oil Drop experiment which determined the magnitude of the negative charge on the electron and the charge to mass ratio, 1/1837 of an H atom Curie and Becquerel: simultaneously discovered radioactivity Curie: discovered Ra and Po using pitcheblende Rontgen: Discovered X-rays Geiger and Marsden: grad students of Rutherford, designed and performed the Gold Foil Experiment trying to find positive thing in atoms Rutherford: Interpreted the results of the Gold Foil Experiment which proved: atoms are mostly empty space, that electrons are within that space, and there is a really dense nucleus with protons, which have a positive charge, nuclear model of the atom Chadwick: working in Rutherford’s lab found the neutron it has no charge and is in the nucleus *********************************************************************** Quantum theory, the behavior of the electron Bohr: said that electrons have energy and that is why the atoms have a color, explained color by electrons jumping up and down from energy levels, when they fall back down they give off light which we see as a certain color, electrons live in energy levels and move around the nucleus on these paths, called planetary model Planck: quantified Bohr’s energy and said that the light given off was a photon, and the leap up to excited state was a quantum of energy E=h =frequency Heisenberg: stated the Uncertainty Principle, you can’t know the speed and location of an electron at the same time DeBroglie: stated that E=mc2 and E=h were equal, E=h says electrons behave like waves of light, E=mc2 says electrons behave like little particles, called the wave-particle duality of electrons Schrodinger: developed the wave equation, electron cloud model of an atom, electrons are in regions of probability called orbitals, wave equation gave 4 quantum numbers for hydrogen’s electron which tell us the size, energy, shape, orientation of orbitals and the spin of the electrons within the orbitals Einstein: E=mc2 Meitner: discovered nuclear fission Fermi: leader of Manhattan project, first controlled nuclear fission reaction Bunsen and Kirchhoff: designed the burner and spectroscope to help identify elements based on the energy of electrons and their bright line emission spectra</p>