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Developing an Atomic Theory

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Title: Developing an Atomic Theory


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
John Dalton
  • 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 example1 g of C combines with 1.333 g of O
    to make carbon monoxide.
  • 1 g of C combines with 2.667 g of O to make
    carbon dioxide.
  • The ratio of O is 12

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 exampleIn 100 g of water, there are 11.11 g
    of H and 88.89 g of O, an HO ratio of 18.
  • In 425 g of water, there are 47.22 g of H and
    377.78 g of O, an HO ratio of 18

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
  • Daltons Atomic Theory.

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

19
John Dalton
  • Daltons 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
  • Daltons 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
  • Daltons 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
J. J. Thomson
  • 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
Robert Millikan
  • Millikan determined the charge of the electron.

33
Robert Millikan
  • He used his oil drop experiment.

34
Robert Millikan
  • He used his oil drop experiment.

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

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

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

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

39
Robert Millikan
  • He became one of the first American scientists to
    win a Nobel Prize in Physics for his work

40
Hantaro Nagaoka
41
Hantaro Nagaoka
  • In 1904, he published a paper where he envisioned
    the Saturnian Model of the atom.

42
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.

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.
  • The electrons would be held in place by
    electrostatic attraction.

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.
  • He eventually abandoned the model in 1908.

45
Ernest Rutherford
46
Ernest Rutherford
  • Rutherford used alpha particles (positively
    charged particles) to explore the structure of
    the atom.

47
Ernest Rutherford
  • He shot these at gold foil and looked at the
    deflection of the particles.

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

49
Ernest Rutherford
  • He was surprised to see that some of the
    particles bounced back at him.

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

?
51
Ernest Rutherford
  • From this data he proposed the solar system
    model of the atom.

52
Ernest Rutherford
  • From this data he proposed the solar system
    model of the atom.

53
Ernest Rutherford
  • From this data he proposed the solar system
    model of the atom.
  • This is the most common view of the atom.

54
Summary
  • There were some in antiquity who postulated the
    existence of atoms.

55
Summary
  • There were some in antiquity who postulated the
    existence of atoms.
  • But, they couldnt provide any demonstration of
    the validity of their claim.

56
Summary
  • John Dalton used experimental results as the
    basis for his theory of atoms.

57
Summary
  • John Dalton used experimental results as the
    basis for his theory of atoms.
  • This was a theory of behavior, not of structure.

58
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.

59
Summary
  • Thomson discovered the electron.

60
Summary
  • Thomson discovered the electron.
  • Rutherford discovered the nucleus.

61
Summary
  • Thomson discovered the electron.
  • Rutherford discovered the nucleus.
  • This led to the solar system model of the atom.

62
Summary
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