1. Chapter 3
History

2. History of the atom Not the history of atom, but the idea of the atom
Original idea Ancient Greece (400 B.C..)

3. Another Greek Aristotle - Famous philosopher
All substances are made of 4 elements
_________________ - Hot
Air - ______________
_________________ - cool, heavy
Water - ___________
Blend these in different proportions to get all substances

4. Who Was Right? What do you think
Greeks settled disagreements by argument
Make your argument

5. Who’s Next? Late 1700’s - John Dalton- England
Teacher- summarized results of his experiments and those of other’s
In Dalton’s ______________ Theory
Combined ideas of elements with that of atoms

6. Dalton’s Atomic Theory
All __________ is made of tiny ___________ particles called atoms.
Atoms of the same element are identical, those of different elements are different.
Atoms of different elements combine in whole number ratios to form __________
Chemical reactions involve the rearrangement of atoms. No new atoms are created or destroyed.

7. Student
Evaluate and discuss one of Dalton’s Postulates.

8. Parts of Atoms _________ - English physicist. 1897
Made a piece of equipment called a ____________________________.
It is a vacuum tube - all the air has been pumped out.

9. Thomson’s Experiment
Voltage source - +
Vacuum tube
Metal Disks

10. Thomsom’s Model Found the __________
Said the atom was like plum pudding
A bunch of positive stuff, with the electrons able to be removed

11. Student Review concept
Summarize what was discovered using the cathode ray tube.

12. Other pieces
Proton - positively charged pieces ___________ times heavier than the electron
Neutron - no charge but the same _____________ as a proton.
Where are the pieces?
William Crookes gets a better vacuum

13. Rutherford’s experiment
Ernest Rutherford English physicist. (1910)
Believed in the plum pudding model of the atom.
Wanted to see how big they are
Used radioactivity
Alpha particles - positively charged pieces given off by uranium
Shot them at gold foil which can be made a few atoms thick

14. Rutherford’s experiment
When the alpha particles hit a florescent screen, it glows.
Here’s what it looked like (pg 84)

15. He Expected
The alpha particles to pass through without changing direction very much
Because
The ______________________ charges were spread out evenly. Alone they were not enough to stop the alpha particles

16. Student check How did Rutherford conclude that he found the proton?
What new discoveries can be made using Rutherford’s experiment

17. Modern View The atom is mostly ___________ __________ Two regions
Nucleus- protons and neutrons
Electron cloud- region where you might find an electron

18. Density and the Atom
Since most of the particles went through, it was mostly empty.
Because the pieces turned so much, the positive pieces were heavy.
Small volume, big mass, big density
This small dense positive area is the __________