2. John Dalton’s Atomic Theory  Elements composed of small particles called “atoms”  All atoms of a given element are the same, but different from other elements  Small, indivisible spheres

3. Rutherford’s Experiment  Kiwi physicist Ernest Rutherford  Shot alpha particles at thin gold foil  alpha particles: –A form of radioactivity (+ charge)  When an alpha particle hits a fluorescent screen, it glows.

4. Lead block Uranium Gold Foil Fluorescent Screen

5. He Expected  The alpha particles to pass through without changing direction very much.

6. What he got

7. How Rutherford explained results  Atom is mostly empty space.  Small dense,positive piece at center. “NUCLEUS”  Alpha particles are deflected by it if they get close enough.

8. J.J. Thompson (1897)  Cathode Ray Tube Experiments Conclusions: Stream of negative charge Named “electrons” Must be some positive charged parts, too.

9. n Passing an electric current makes a beam appear to move from the negative to the positive end Thompson’s Experiment Voltage source +-

10. Thompson’s Experiment n By adding an magnetic field he found that the moving pieces were negative + -