1. Atomic Theory Democritus – Continuous Theory Separate, discrete particles Cannot be further divided Called them Atoma Atom came from it Law of definite composition Every compound is formed of elements combined in specific ratios by mass unique for that compound

2. Atomic Theory Dalton – 1803 Combinations of different atoms form compounds Atoms of different elements have different masses Made first atomic table Revised into periodic table of elements Dalton’s model foundation of modern atomic theory

3. Atomic Theory Thomson – Electron Discovery Cathode ray beam unaffected by gravity Must be wave Affected by magnetism Must be charged Drawn to positive charge – must be negatively charged particles Stoney called electrons

4. Atomic Theory Thomson – Plum pudding model Mass of charged particles almost nothing, but entire atom mass a lot more Negatively charged particles embedded in positively charged substance (pudding) that completely surrounds them – neutral charge

5. Atomic Theory Rutherford/Geiger and the Nucleus Alpha particles – mass of 7300 electrons Pass through gold foil, strike zinc sulfide, flash of light Some deflected, some ricocheted! They must be hitting something massive! http://www.youtube.com/w atch?v=QY8w8xpKKzs http://www.youtube.com/w atch?v=QY8w8xpKKzs

6. Atomic Theory Rutherford/Geiger and the Nucleus Later discovered that nucleus positively charged – named positive particles protons 1836 times more massive than electrons # of protons in nucleus Atomic number

7. Atomic Theory Chadwick and the Neutron Nuclei more massive than protons yet positively charged Must be neutral particles Particles named neutrons Electrons orbit much like planets

8. Atomic Theory Bohr-Electron energy levels Why orbits not decay? Heated elements produce spectra – lines of emissions Electrons exist in specific energy levels, as energy absorbed, move from one level to another (quantize) for short period, when return, emit light in specific spectra

9. Atomic Theory Bohr-Electron energy levels 6 or 7 levels per atom Spectra unique to each element Note the spectra, identify the element

10. Atomic Theory Modern Quantum Theory – DeBroglie’s Hypothesis Electrons orbit in waves – not continuous round motion Always complete wave, never partial

11. Atomic Theory Modern Quantum Theory - Heisenberg’s uncertainty principle Electrons orbit in 4 dimensions (time) their position at any point in time cannot be precisely determined! Orbit in clouds

12. Atomic Theory Physicist humor