1. Developing an Atomic Theory Part I

2. The Greeks Aristotle considered matter to be “continuous,” that is, it could be infinitely divided.

3. The Greeks Democritus argued that all matter was composed of small, indestructible particles called “atoms.”

4. The Greeks Neither of these men were experimentalists and could not show any evidence to support their hypotheses.

5. The Greeks Neither of these men were experimentalists and could not show any evidence to support their hypotheses. However, Aristotle could at least argue that matter looked continuous as we sliced something (like cheese) thinner and thinner.

6. John Dalton

7. He studied the results of chemical experimentation.

8. John Dalton He studied the results of chemical experimentation. The Law of Multiple Proportions

9. John Dalton He studied the results of chemical experimentation. The Law of Multiple Proportions “Whenever the same two elements form more than one compound, the different masses of one element that combine with the same mass of the other element are in the ratio of small whole numbers.”

10. John Dalton He studied the results of chemical experimentation. The Law of Multiple Proportions For example:1 g of C combines with 1.333 g of O to make carbon monoxide1 g of C combines with 2.667 g of O to make carbon dioxideThe ratio of O is 1:2

11. John Dalton He studied the results of chemical experimentation. The Law of Definite Proportions

12. John Dalton He studied the results of chemical experimentation. The Law of Definite Proportions “In samples of any chemical compound, the masses of the elements are always in the same proportions.”

13. John Dalton He studied the results of chemical experimentation. The Law of Definite Proportions For example:In 100 g of water, there are 11.11 g of H and 88.89 g of O, an H:O ratio of 1:8In 425 g of water, there are 47.22 g of H and 377.78 g of O, an H:O ratio of 1:8

14. John Dalton He arrived at his own atomic theory.

15. John Dalton He arrived at his own atomic theory. The theory described how atoms act.

16. John Dalton He arrived at his own atomic theory. The theory described how atoms act. It did not describe the structure of the atom.

17. John Dalton Dalton’s Atomic Theory.

18. John Dalton Dalton’s Atomic Theory. All elements are composed of tiny indivisible particles called atoms.

19. John Dalton Dalton’s Atomic Theory. All elements are composed of tiny indivisible particles called atoms. Atoms of the same element are identical and the atoms of any one element are different from the atoms of any other element.

20. John Dalton Dalton’s Atomic Theory. Atoms of different elements can physically mix together or can chemically combine in simple whole-number ratios to form compounds.

21. John Dalton Dalton’s Atomic Theory. Atoms of different elements can physically mix together or can chemically combine in simple whole-number ratios to form compounds. Chemical reactions occur when atoms are separated, joined, or rearranged. Atoms of one element, however, are never changed into atoms of another element as a result of a chemical reaction.

22. J. J. Thomson

23. Thomson discovered that the atom was not a solid sphere.

24. J. J. Thomson Thomson discovered that the atom was not a solid sphere. He used a cathode ray tube to show the that atoms were (at least partially) composed of negatively charged particles called electrons.

25. J. J. Thomson Thomson discovered that the atom was not a solid sphere. He used a cathode ray tube to show the that atoms were (at least partially) composed of negatively charged particles called electrons.

26. J. J. Thomson Thomson discovered that the atom was not a solid sphere. From this data, he postulated the “raisin pudding” model of the atom in 1897.

27. J. J. Thomson Thomson discovered that the atom was not a solid sphere. The atom is a sphere of positive charge...

28. J. J. Thomson Thomson discovered that the atom was not a solid sphere. The atom is a sphere of positive charge...

29. J. J. Thomson Thomson discovered that the atom was not a solid sphere. The atom is a sphere of positive charge with negatively charged electrons imbedded in the sphere.

30. J. J. Thomson Thomson discovered that the atom was not a solid sphere. The atom is a sphere of positive charge with negatively charged electrons imbedded in the sphere.

31. Robert Millikan

32. Millikan determined the charge of the electron. Robert Millikan

33. He used his “oil drop” experiment. Robert Millikan

34. He used his “oil drop” experiment. Robert Millikan

35. He used his “oil drop” experiment. Oil was sprayed into a chamber and allowed to fall into a charging chamber. Robert Millikan

36. He used his “oil drop” experiment. The oil drops were charged (ionized) between two charged plates with x-rays. Robert Millikan

37. He used his “oil drop” experiment. The speed of the oil drops were dependent on the charge of the drops. Robert Millikan

38. He used his “oil drop” experiment. After thousands of experiments, Millikan determined the charge of the electron. Robert Millikan

39. He used his “oil drop” experiment. After thousands of experiments, Millikan determined the charge of the electron. Robert Millikan

40. He became one of the first American scientists to win a Nobel Prize in Physics for his work Robert Millikan

41. Hantaro Nagaoka

42. In 1904, he published a paper where he envisioned the “Saturnian Model” of the atom.

43. Hantaro Nagaoka In 1904, he published a paper where he envisioned the “Saturnian Model” of the atom. In this model, the electrons of the atom circled a massive nucleus.

44. Hantaro Nagaoka In 1904, he published a paper where he envisioned the “Saturnian Model” of the atom. In this model, the electrons of the atom circled a massive nucleus. The electrons would be held in place by electrostatic attraction.

45. Hantaro Nagaoka In 1904, he published a paper where he envisioned the “Saturnian Model” of the atom. In this model, the electrons of the atom circled a massive nucleus. The electrons would be held in place by electrostatic attraction. He eventually abandoned the model in 1908.

46. Ernest Rutherford

47. Rutherford used alpha particles (positively charged particles) to explore the structure of the atom.

48. Ernest Rutherford He shot these at gold foil and looked at the deflection of the particles.

49. Ernest Rutherford He shot these at gold foil and looked at the deflection of the particles.

50. Ernest Rutherford He was surprised to see that some of the particles bounced back at him.

51. Ernest Rutherford He was surprised to see that some of the particles bounced back at him. ?

52. Ernest Rutherford He was surprised to see that some of the particles bounced back at him. ?

53. Ernest Rutherford From this data he proposed the “solar system” model of the atom.

54. Ernest Rutherford From this data he proposed the “solar system” model of the atom.

55. Ernest Rutherford From this data he proposed the “solar system” model of the atom. This is the most common view of the atom.

56. Summary There were some in antiquity who postulated the existence of atoms.

57. Summary There were some in antiquity who postulated the existence of atoms. But, they couldn’t provide any demonstration of the validity of their claim.

58. Summary John Dalton used experimental results as the basis for his theory of atoms.

59. Summary John Dalton used experimental results as the basis for his theory of atoms. This was a theory of behavior, not of structure.

60. Summary John Dalton used experimental results as the basis for his theory of atoms. This was a theory of behavior, not of structure. Dalton knew how atoms would react but not what in the structure allowed that reaction.

61. Summary Thomson discovered the electron.

62. Summary Thomson discovered the electron. Rutherford discovered the nucleus.

63. Summary Thomson discovered the electron. Rutherford discovered the nucleus. This led to the “solar system” model of the atom.

64. Summary