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Atomic Theory
Chemistry
Mrs. Ginn
Early Models
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Democritus
Greek philosopher
4th Century BC
Coined the term atom
Believed atoms are
indivisible and
indestructible
Approach not based on
scientific method
Early Models
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John Dalton
1766- 1844
English chemist and
teacher
Experimental methods
Dalton’s Atomic Theory
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All elements are composed
of atoms
Atoms of the same element
are identical
Atoms of different elements
can mix and combine in
whole number ratios to form
compounds
Chemical reactions occur
when atoms are separated,
Early Models
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J. J. Thomson
1856-1940
Cathode Ray Experiment
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An electrical current
passed through a gas at
low pressure “bent” the
cathode ray toward a (+)
charged metal plate
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Discovered the electron
Plum-pudding Model
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Electrons evenly
distributed
Early Models
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Robert Millikan
1868-1953
Taught physics
Worked with Harvey Flethcher
on
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Oil Drop Experiment
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Charge carried by positive and
negative entities
Received Nobel Prize in 1923
Early Models
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Ernest Rutherford
1871-1937
• Gold Foil Experiment
• Atoms are mostly empty
space surrounding a
dense nucleus
• Discovered the nucleus
4-Square
Include all of the following information as well as a colored
picture of the experiment
Name: Dalton
Name: Thomson
Experiment
Experiment
Results
Results
Name: Millikan
Name: Rutherford
Experiment
Experiment
Results
Results