1. The student will learn:
1. Development of modern day Atomic theory
2. Early contributions of Democritus/Dalton
3. Discovery of electron: Thompson/Millikan
4. Discovery of nucleus: Rutherford/Chadwick

2. History of the Atomic TheoryBC
Democritus: small invisible particles called atomos.
How?

3. Dalton’s Atomic theory
John Dalton Englishman
Dalton’s Atomic theory
1. element made up tiny particles called atoms
2. atoms of a given element are identical
Ex) all carbon atoms have same physical & chemical properties
atoms of a different element are different in some way
Ex) carbon atoms have different physical & chemical properties than sulfur

4. Dalton’s Atomic Theory
3. Atoms of one element combine with atoms of a different element to form Compounds.
* Law of Definite Proportion
All samples of a compound contain the same ratio / or / proportion of the elements
* Chemical Formulas

5. Dalton’s Atomic Theory
4.Chemical reactions involve reorganization of atoms
* atoms are not changed just rearranged
* atoms of one element cannot change into atoms of another element.
“ cannot change copper into gold”

6. Dalton’s Atomic Theory

7. 1st discovery of subatomic particles Discovery of electrons
1897 J.J.Thomson : used a cathode ray tube

8. Discovery of electrons
Caused a vacuum in tube
Filled it with a gas
A piece of metal at each end + / -
Put electricity through it
Surface opposite the cathode+ glowed
Put magnets next to it = caused a deflection
Placed an object inside it cast a shadow
Placed a wheel inside and it moved

9. Thomson’s Plum Pudding model of an atom. Idea of the time…
Thomson’s Plum Pudding model of an atom. Idea of the time….William Thomson aka…. Lord Kelvin

10. JJ Thomson 1897

11. Robert A. Millikan American physicist- 1909
Charge of electron x coulomb
Oil drop experiment: suspended an oil drop between two charged plates.

13. If made of pieces……..
then should be able to break it into pieces……..
Discovery of Nucleus
Ernst Rutherford
Gold foil experiment:
Bombarded a piece of gold foil with alpha particles which were considered positive.
Expected to go all the way through it.

14. Results of foil experiment if Plum Pudding model had been correct.

15. Rutherford’s experiment.

16. Actual results.

17. Thought about for 2 years.
p.72
“as if you had fired a 15 inch artillery shell at a piece of tissue paper and it bounced back”.
Ernst Rutherford
Thought about for 2 years.
Rebounded positive 2He atom means Gold must have a dense middle and be positive.
Named it nucleus and it must be positive.

18. Ernest Rutherford

19. James Chadwick discovery of neutron
In 1913 he was in Germany at start of World War I and would be interned in Ruhleben P.O.W. camp just outside of Berlin.
Hans Geiger and Ernest Rutherford interceded for his release.
It was his discovery of neutrons that led to “nuclear fission”…….sleeping pills

20. Sir James Chadwick English - 1913

21. Electrons from J.J.Thomson 1897 Nucleus from Rutherford 1911
Atoms from Dalton
Electrons from J.J.Thomson 1897
Nucleus from Rutherford 1911
Neutron from Chadwick 1932
Protons????
Collaborative but assigned to Rutherford….because needed something positive to make neutral.

23. What was discovered and who discovered it in the following photo?

24. Who & what was discovered?