1. History of the Atomic Theory
Unit 3 L.1 The Atom

2. Aristotle & other Early Thinkers….
Thought all things (matter) was made up of the 4 “elements” – earth, water,
air, & fire

3. Democritus, 440 B.C. Greek Philosopher

4. First Theory Proposed – Explain the quote:
“The material cause of all things that exist is the coming together of atoms and void.”

5. Democritus proposed that:
Atoms are the “uncuttable” particle.
Name comes from “atomos” (Greek for “Indivisible”)
Atoms are always moving
(~ Brownian motion)

6. Why his ideas were not accepted
Aristotle did not accept atoms because you could not observe them
No experiments!
It took over 2000 years for this idea to re-emerge

7. 1. John Dalton (1808) (The Age of Enlightenment!)
Other scientists had shown that matter is conserved(Lavoisier), and that substances combine in a set ratio(Proust):
e.g. water = 2 H’s and 1 O always
Dalton asked “WHY?”
He also came up with the Law of Multiple Proportions, as well a Dalton’s Atomic Theory.
He experimented, & produced empirical data!

8. Dalton’s Atomic Theory
All substances are made of atoms.

9. 2. Atoms cannot be
created, divided nor destroyed.
3. Atoms of the same element are exactly alike
4. Atoms join with other atoms to make new substances

10. Dalton’ Atom model. Basically, a tiny solid ball, different sizes
for the
different
elements.

11. "Daltons symbols". Licensed under Public Domain via Commons -

12. 2. J. J. Thomson-1897
Worked with a Cathode Ray Tube

13. Cathode Ray(Crookes) Tube
"JJ Thomson Crookes Tube Replica" by Kurzon - Own work. Licensed under CC BY-SA 3.0 via Commons -
The cathode rays (blue) were emitted from the cathode, sharpened to a beam by the slits, then deflected as they passed between the two electrified plates.

14. Thomson’s Conclusions
Atoms are not the smallest particle! They are divisible!
They are made up of negatively charged particles(corpuscules) embedded in positively charged matrix(the pudding).
Atoms are neutral.
All elements used showed the same results!

15. Thomson’s Atomic Theory
The “Plum Pudding” Model
The atom is mostly positively charged matrix with small, negatively charged particles, corpuscles, embedded throughout

16. The Plum Pudding Model
Or negative corpuscles
Matrix

17. Or like Chocolate chip ice-cream….(yum!)

18. Homework 
Copy labeled diagrams of Thomson’s Experiment and Atom Model.

19. Homework  Copy and Answer the following in yr ntbk
What discovery demonstrated that atoms are not the smallest particles?
What did Dalton do in developing his theory that Democritus did not do?
Analyzing Methods. Why was it important for Thompson to repeat his experiment?

20. E.R. Ernest Rutherford (1909) About the Gold Foil Experiment,
“It was quite the most incredible event that has ever happened to me in my life.”
E.R.

24. Top: Expected results: alpha particles passing through the plum pudding model of the atom undisturbed. Bottom: Observed results: a small portion of the particles were deflected, indicating a small, concentrated positive charge. Note that the image is not to scale; in reality the nucleus is vastly smaller than the electron shell.

25. Rutherford’s Conclusions
The atom is mostly empty space! (The void!)
There is a positively charged center to the atom

26. Rutherford's Atom Model

27. Compare Thompson’s & Rutherford’s Models
"Geiger-Marsden experiment expectation and result" by Kurzon - Own work. Licensed under CC BY-SA 3.0 via Commons -

28. James Chadwick -
Discovered Neutrons – neutral particles in the nucleus(center)
Was Rutherford’s student.

29. The Bohr (Planetary) Model
Electrons travel around the nucleus in definite paths, or orbits
Each path/orbit is located in levels at certain distances
Electrons can jump from one path(energy level) to the next), but can’t stay in between paths
Like a ladder!

30. Bohr’s Planetary Model

31. The Modern Theory: Think of bees around a beehive……!
Electrons do not follow defined paths, but move in ‘regions’ around the nucleus
Exact path and location of an electron is not known. Regions are where electron is “likely” to be found
These regions are called
“electron clouds”
Think of bees around a beehive……!

32. "Helium atom QM" by User:Yzmo - Own work. Licensed under CC BY-SA 3
"Helium atom QM" by User:Yzmo - Own work. Licensed under CC BY-SA 3.0 via Commons -

33. The Schrödinger and Heisenberg MODERN Cloud Model

35. Classwork  Copy and answer in notebook
In what part of an atom is most of its mass located?
What are 2 differences between the atomic theory described by Thomson and that described by Rutherford?
Comparing Concepts. Identify the difference in how Bohr’s theory and the Modern theory describe the location of electrons.

36. Give 2 similarities and 2 differences between
Compare and Contrast
Give 2 similarities and 2 differences between
J.J. Thompson’s Model and The Modern Model of the Atom

37. Classwork and Homework 
Do all questions in text p
Not the Lesson Review.