1. Chapter 4: Atomic Structure
Table of Contents
Chapter 4: Atomic Structure
Atomic History
Democratis
Dalton
Johnson
Rutherford
Bohr

2. Democritus First to theorize about the atom in 400 B. C.
The string analogy

3. Development of the Modern Atomic Theory
Lavoisier - law of conservation of matter
Dalton - atomic theory of matter – explains the observations of Lavoisier & others
Burning steel wool

5. 1897 – J.J. Thomson – Cathode Ray Tube discovered the electron.
Tesla coil

6. Cathode Ray
Why does the beam deflect?

7. + Cathode-Ray Tube electrodes vacuum
- With charge, opposites attract, similar repels
- Rays bent toward positively charged plate & away from negatively charged plate
Charged electrodes → rays flow from one electrode to the other TV

8. Cathode-Ray Tube
Conclusions from Thomson’s Cathode-Ray Tube:
Discovered electrons: negatively charged particles
These electrons had to come from atoms
Atoms can’t be entirely negatively charged so… Plum Pudding Model

9. Rutherford’s Gold Foil Experiment
Ernest Rutherford – Gold Foil Experiment

10. Gold Foil Experiment What were the 3 paths of the particles?
What was discovered?

11. The Gold Foil Experiment
coated with zinc sulfide, which glows when struck by the positively charged particles of the beam

12. 2 1 3 Discoveries from Rutherford’s Gold Foil Experiment
Atoms are mostly space
Atoms contain a dense center (nucleus)
The nucleus is positively charged

13. Niels Bohr
Proposed that electrons must have enough energy to keep them in constant motion around the nucleus.
Electrons can move from one path to another by taking in or letting off energy
1913 – Bohr – Planetary Model

14. Evidence for Energy Levels
Electrons can have only certain amounts of energy & orbit around nucleus
Energy levels: The regions of space in which electrons can move around the nucleus of an atom

15. The emission spectrum of an element: The spectrum of light released from excited atoms

16. Other Particles
Rutherford discovered the positively charged proton in the center of the atom
James Chadwick discovered the neutron – another particle in the atom’s center with no charge but a similar mass to the proton.

17. The Electron Cloud Model
20th century – energy levels are not organized like planets
Energy levels are spherical regions of space around the nucleus in which electrons are most likely to be found.
e- are tiny and move quickly through space
Electron cloud: The space around the nucleus of an atom where the atom’s electrons are found

18. The Electron Cloud Model

19. Review: identify each model
Thomson’s
Plum-Pudding Model
Bohr’s
Planetary Model
Present
Electron Cloud Model