1. Atomic Structure- Part II
Honors Chemistry
Mrs. Coyle

2. Discoveries of the Electron, the Proton and the Charge of the Electron

3. History Electron means “amber” in Greek.
Properties discovered by the Greek Thales of Miletos (600 BC). Rubbed the mineral amber with cat fur and attracted feathers.

4. Benjamin Franklin (America 1740’s)
Law of conservation of charge.
Saw electricity as a flowing fluid and called the flow direction positive.

5. Law of Charges
Like charges repel
Opposite charges attract

6. J(oseph) J(ohn) Thomson (England 1897)
He discovered the electron while experimenting with cathode rays.

7. Cathode Ray

8. Video Link CRT

9. Deflection of Cathode Ray

10. Cathode Ray Tube

11. JJ Thomson with the CRT

12. Thomson’s Discovery
He determined that the cathode ray was made of negatively charged particles – electrons.

13. Cathode Rays
Thomson also was able to estimate that the mass of the electron was equal to about 1/1840 of the mass of a hydrogen atom.
His discovery of the electron won the Nobel Prize in 1906.

14. Cathode Rays
Thompson showed that the production of the cathode ray was not dependent on the type of gas in the tube, or the type of metal used for the electrodes.
He concluded that these particles were part of every atom.

15. Robert Millikan (USA, 1916)
Measured the charge of the electron with the “Oil Drop” experiment. (Nobel Prize 1923)

17. Link to Video: Millikan’s Oil Drop Experiment

18. Millikan’s Oil Drop Experiment+ e -
He found the charge of the electron e = x C (Coulombs), by noting that the droplets always carried whole number multiples of that number.

19. Charge of the Electron Charge of Electron 1.6 x 10-19 C (coulombs)
Mass of Electron
9.11 x g

20. Atoms have no net electric charge.

21. Ions Positively charge atom (cation) Negatively charged atom (anion)
Atom lost electrons.
Negatively charged atom (anion)
Object gained electrons.

22. The Electron is the basic quantity of charge.
Electric charges always exist in whole number multiples of a single basic unit, the electron.

23. A particle with a positive charge must be present in the atom to balance each negatively charge electron.

24. Plum Pudding Model (Thomson)

25. Application of the CRT

26. Why is watching television potentially unsafe?

27. The Discovery of the Proton
Discovered by Eugen Goldstein (German) in 1886.
He observed “Canal Rays” and found that they are composed of positive particles – protons.

28. Canal Rays
Canal Rays passed through holes, or channels, in the reverse direction as the cathode ray. 

29. Canal Rays