Atomic Theory

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#1 Democritus
(460-370)

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Contribution to atomic theory: believed that atoms were indivisible. He suggested the overall existence of atoms.
Faults in his theory: Atom isn't a sphere or a solid; atoms are composed of mostly empty space.
Believed? No because he wasn't well known and did not have any experimental proof.

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#2 Aristotle
(384-322)

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Contribution to Atomic Theory: Believed there to be only 5 elements. (Air, Earth, Water, Fire, and Aether). Believed matter was infinitely divisible.
Believed?: Yes because Aristotle had previous theories and observations that led to great scientific advancements and was therefore virtually unquestioned.
Other: Tutored Alexander the Great

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#3 John Dalton
(1766-1844)

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Contribution to atomic theory: Wrote the four postulates of atomic theory: 1)When atoms combine, separate, or rearrange a reaction will occur. 2) Atoms are indestructible and indivisible. 3) Elements of the same substance are identical. 4) Compounds are formed by a combination of two or more different kinds of atoms.
Other: Alchemy is impossible because of these postulates.
Flawed: because isotopes exist

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#4 Antoine Lavoisier
(1789)

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Contribution to atomic theory: Law of conservation and mass
Other: discovered oxygen

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#5 Joseph Proust
(1754-1826)

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Contribution to atomic theory: Law of definite proportions

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#6 Sir JJ Thomson
(1856-1940)

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Contribution to atomic theory: he was able to identify the existence of electrons in an atom. The meant that atoms are not invisible and could be seen.
Experiment:Plum Pudding(i.e. chocolate chip cookie dough) & Cathode Ray Experiment- A gas filled tube with electrodes which which related to electricity which showed atoms have a charge.
Further tests: Mass to charge ratio and Different gasses.

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#7 Rutherford
(1871-1937)

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Contribution to atomic theory: Discovered that atoms are composed of mostly empty space and this is why alpha particles can not pass through it. DISCOVERED THE NUCLEUS where all the positive charge and most of the mass is located.
Experiment: Gold foil experiment shot alpha particles through thin gold and they passed through it.

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#8 Goldstein

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