1. Atomic Theory

2. The Atom Recall the atom is the smallest particle making up an element

3. Evolution of the Atom Our ideas about the nature of atoms have progressed over the last two centuries (and continue to develop today). There are a few scientists who’s works have contributed to our current knowledge of the atom.

4. JJ Thomson Year 1900 Discovered the electron Thomson proposed raisin bun model… Described the atom as positively charged sphere of matter with negative electrons dispersed throughout electrons=raisins, positive mass=dough MODELTHOMSON (1900) DIAGRAM

5. Raisin Bun

6. Ernest Rutherford Year 1910 Rutherford proposed the nuclear model …. Described the atom as having a central positive nucleus (core) surrounded by negative orbiting electrons MODELRUTHERFORD (1910) DIAGRAM

7. Nuclear Model

8. Proof?

9. Rutherford’s Famous Gold Foil Experiment A beam of positively charged alpha particles are aimed at a thin sheet of gold foil (source radioactive radium)

10. Rutherford expected that the positive particles would pass through the sheet of gold foil since years earlier Thomson proposed that mass of the atom was evenly dispersed throughout the atom.

11. MOST of the alpha particles did go straight through the gold foil with NO deflection.

12. 1. However a small hand full of particles were deflected from original path.

13. This could only happen if the the particles hit something that had substantial mass and size and then bounced off at an angle.

14. Rutherford’s experiment PROVED the presence of a dense, positively charged core called the nucleus which was surrounded by mostly empty space and orbiting electrons.

15. Niels Bohr Year 1911 Bohr proposed the planetary model …. Nucleus (core) contains protons and neutrons but electrons are located in specific regions around the nucleus MODELBOHR (1911) DIAGRAM

16. 1. Solar System Like planets are at a defined distance from Sun

17. In each of the 3 boxes on the lower half of your sheet, make the following headings: location charge symbol mass

18. Location Charge Symbol Mass orbitals negative e- e- 1/1800 amu Electron

19. Location Charge Symbol Mass nucleus positive p+ p+ 1 amu Proton 1 atomic mass unit (amu) = 1.67 x -24 g 1 amu = 0.00000000000000000000000000000167 g

20. Location Charge Symbol Mass nucleus neutron n0 n0 1 amu Proton 1 atomic mass unit (amu) = 1.67 x -24 g