The Rutherford's Gold Foil — Transcript

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1. 0:00Rutherford's Atomic Model
2. 0:05“Indigo blue is extracted from the indigo plant
3. 0:07but is bluer than the plant it comes from”
4. 0:10is a remarkable Chinese proverb
5. 0:11that captures the essence of a student outshining the teacher
6. 0:15A historic example happened in the field of chemistry,
7. 0:18when Ernest Rutherford, hailed as the “Father of Nuclear Physics”,
8. 0:21surpassed the prowess of his own mentor, J. J. Thomson,
9. 0:24by providing a profound and superior understanding
10. 0:27of atomic structure
11. 0:29As we previously learned,
12. 0:30atoms consist of three main components:
13. 0:32protons, neutrons, and electrons
14. 0:35These components were not all discovered at once,
15. 0:37but rather through a series of hypotheses and experiments
16. 0:40that led to revisions of the atomic models
17. 0:43The early atomic model was proposed by J. J. Thomson in 1897,
18. 0:47following the discovery of the electron and its mass
19. 0:50Thomson hypothesized that
20. 0:52the negatively charged electrons in an atom
21. 0:54should be counterbalanced by positive charges
22. 0:56to make the atom electrically neutral
23. 0:59Therefore, he suggested a “Plum Pudding” atomic model
24. 1:02He postulated that electrons are embedded
25. 1:05in a lump of positively charged cloud,
26. 1:07similar to raisins spread in plum pudding
27. 1:09While this model succeeded in explaining the atom's neutrality,
28. 1:13it hatched other questions, such as:
29. 1:15how could two opposite charges coexist in an atom
30. 1:18without being unstable?
31. 1:19And since it is known that electron mass is so tiny,
32. 1:23then what makes up the atomic mass?
33. 1:25Ernest Rutherford, who was once a protege of Thomson
34. 1:27at Cavendish Laboratory,
35. 1:29sought to answer these questions
36. 1:30through his gold foil experiment in 1909
37. 1:33Together with his coworkers,
38. 1:35Hans Geiger and Ernest Marsden,
39. 1:37he conducted an experiment
40. 1:39in which a sample of radium was stored in a plumber box
41. 1:41with a very small hole,
42. 1:43emitting positively charged alpha particles through it
43. 1:46The box was positioned in line with the thin gold foil
44. 1:49that was surrounded by a zinc-sulfide screen
45. 1:51While the alpha particles from the radium
46. 1:54hit the gold foil,
47. 1:55they scattered
48. 1:56and produced light flashes that were detected
49. 1:58by the screen
50. 1:59Based on the plum pudding model,
51. 2:01Rutherford thought that most of the particles
52. 2:03would pass through the foil,
53. 2:04while some are slightly deflected due to their encounter with electrons
54. 2:08Initially, the experiment results were indeed consistent
55. 2:11with his assumption
56. 2:12But what followed next was totally unexpected!
57. 2:15Some particles encountered large-angle deflections
58. 2:18and very few (about 1 in every 20,000)
59. 2:21were bounced backward!
60. 2:23Rutherford thought there must be something
61. 2:25positive, minuscule, yet heavy
62. 2:27in the center of gold atoms that repels positive alpha particles
63. 2:31and essentially makes up the atomic mass!
64. 2:33He called it the atom’s nucleus
65. 2:35This result strengthened the previous notion
66. 2:38about the existence of positively charged particles
67. 2:41later known as protons –within atoms
68. 2:43And since the majority of the particles passed through,
69. 2:46he suggested that an atom is mostly empty space
70. 2:49Rutherford proposed an atomic model
71. 2:51named "The Nuclear Model"
72. 2:53based on this inquiry
73. 2:54He stated that there is a tiny nucleus
74. 2:56with positively charged particles inside
75. 2:58and it is surrounded by electrons
76. 3:00Different elements have different numbers of protons
77. 3:03But in one atom,
78. 3:04the proton amount is equal to the number of electrons
79. 3:07revolving around the nucleus, making the atom neutral
80. 3:11This model satisfyingly answered the questions
81. 3:13that plum pudding model couldn’t explain,
82. 3:15but it contradicts the principle of classical electrodynamics
83. 3:19According to the principle,
84. 3:20a charged particle in circular motion radiates energy continuously
85. 3:25The electrons in this model move in circular motion
86. 3:27and lose energy, causing them to spiral toward the center,
87. 3:31and resulting in the collapse of the atom
88. 3:33Yet in fact, none of these things happen
89. 3:35Additionally, the energy-radiating particle
90. 3:38must form a continuous atomic spectrum,
91. 3:40but the observation showed a line spectrum
92. 3:43Despite the limitations,
93. 3:45Rutherford’s model provided a fundamental understanding
94. 3:48of atomic structure,
95. 3:49His intensive research about atoms and initial discovery
96. 3:52awarded him the Nobel Prize
97. 3:54We are still halfway through our journey on atomic model development
98. 3:58In the upcoming video, as you guess,
99. 4:00we’ll move forward a few years later to discuss the next model
100. 4:03and how it helps refine Rutherford’s idea!
101. 4:09Thank you for your continuous support!
102. 4:11Especially our valued patrons and members
103. 4:13who have been encouraging us
104. 4:15to keep producing more quality contents!