Atomic history day #2 1
- 1. Ernest Rutherford (1871-1937) Learned physics in J.J. Thomson lab. Noticed that alpha particles were sometime deflected by something in the air. Gold-foil experiment
- 2. Rutherford Scattering In 1909 Rutherford undertook a series of experiments He fired (alpha) particles at a very thin sample of gold foil According to the Thomson model the particles would only be slightly deflected Rutherford discovered that they were deflected through large angles and could even be reflected straight back to the source Lead collimator Gold foil particle source
- 3. Rutherfords Apparatus beam of alpha particles radioactive substance fluorescent screen circular - ZnS coated gold foil Dorin, Demmin, Gabel, Chemistry The Study of Matter , 3rd Edition, 1990, page 120
- 4. What he expected California WEB
- 5. Because he thought the mass was evenly distributed in the atom. - - - - -
- 6. Because, he thought the mass was evenly - - distributed in the atom - - - - - - - - - - - - - - - - - - - - - - -
- 7. What he got
- 8. Density and the Atom Since most of the particles went through, the atom was mostly empty. Because the alpha rays were deflected so much, the positive pieces it was striking were heavy. Small volume and big mass = big density This small dense positive area is the nucleus California WEB
- 9. The Rutherford Atom n+ Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 57
- 10. Niels Bohr In the Bohr Model (1913) the neutrons and protons occupy a dense central region called the nucleus, and the electrons orbit the nucleus much like planets orbiting the Sun. They are not confined to a planar orbit like the planets are.
- 11. Bohr Model Planetary model After Rutherfords discovery, Bohr proposed that electrons travel in definite orbits around the nucleus.