Chapter 1

1. Chapter 1 Atoms and their structure

2. History of the atom • Not the history of atom, but the idea of the atom • Original idea Ancient Greece (400 B.C..) • Democritus and Leucippus Greek philosophers

3. History of Atom • Smallest possible piece? • Atomos - not to be cut • Looked at beach • Made of sand • Cut sand - smaller sand

4. Another Greek • Aristotle - Famous philosopher • All substances are made of 4 elements • Fire - Hot • Air - light • Earth - cool, heavy • Water - wet • Blend(Mix) these in different proportions to get all substances

5. Boyle • Was Irish scientist • Introduced the first definition for the element The element: is pure form of matter can’t be simplified into more simpler by normal chemical process

6. Dalton’s Atomic Theory • All matter is made of tiny indivisible particles called atoms. • Atoms of the same element are identical, those of different atoms are different.

7. Parts of Atoms • J. J. Thomson - English physicist. 1897 • Made a piece of equipment called a cathode ray tube. • It is a vacuum tube - all the air has been nearly pumped out. pressure inside is 0.01mmHg

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

9. Voltage source Thomson’s Experiment - +

10. Voltage source Thomson’s Experiment - +

11. Voltage source Thomson’s Experiment - +

12. Voltage source Thomson’s Experiment - + • Passing an electric current makes a beam appear to move from the negative to the positive end

13. Voltage source Thomson’s Experiment - + • Passing an electric current makes a beam appear to move from the negative to the positive end

14. Voltage source Thomson’s Experiment - + • Passing an electric current makes a beam appear to move from the negative to the positive end

15. Voltage source Thomson’s Experiment - + • Passing an electric current makes a beam appear to move from the negative to the positive end

16. Voltage source Thomson’s Experiment • By adding an electric field

17. Voltage source Thomson’s Experiment + - • By adding an electric field

18. Voltage source Thomson’s Experiment + - • By adding an electric field

19. Voltage source Thomson’s Experiment + - • By adding an electric field

20. Voltage source Thomson’s Experiment + - • By adding an electric field

21. Voltage source Thomson’s Experiment + - • By adding an electric field

22. Voltage source Thomson’s Experiment + - • By adding an electric field he found that the moving pieces were negative

23. Thomsom’s Model • The atom is homogenous sphere of positive charge inside it electrons are inserted

24. Rutherford’s experiment • Ernest Rutherford English physicist. (1910) • Believed in the Thomson’s 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

25. Rutherford’s experiment • When the alpha particles hit a florescent screen, it glows. • Here’s what it looked like (pg 72)

26. Florescent Screen Lead block Uranium Gold Foil

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

28. What he expected

29. Because

30. Because, he thought the mass was evenly distributed in the atom

31. Because, he thought the mass was evenly distributed in the atom

32. What he got

33. + How he explained it • Atom is mostly empty • Small dense, positive piece at center • Alpha particles are deflected by it if they get close enough

34. +