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Chp. 4 Atomic Theory History Democritus proposes the first atom. He says it is a small, hard particle made of a single material formed into different shapes and sizes. Claimed that atoms are always moving and that they form different materials by joining together.
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Chp. 4 Atomic Theory History John Dalton proposes the first atomic theory in the late1700’s and early 1800’s. Dalton was at first met with resistance but his theory is accepted by the end of the nineteenth century.
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Chp. 4 Atomic Theory History Dalton’s theory is as follows: All substances are made of atoms. Atoms are small particles that cannot be created, divided, or destroyed. Atoms of the same element are exactly alike, and atoms of different elements are different. Atoms join with other atoms to make new substances.
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Chp. 4 Atomic Theory History
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J.J. Thomson (1897) discovered small particles inside the atom. He called the negatively charged particles “corpuscles”, but we now call them electrons. He proposed a model to the atom that is called the “plum-pudding” model. Said that the atom is a positively charged blob and the negative electrons are scattered throughout.
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Chp. 4 Atomic Theory History
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Ernest Rutherford proposes a new atomic theory in 1909. Experimented with atoms by “shooting” positive particles at gold foil. Found that electrons move in space around the dense positive nucleus.
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Chp. 4 Atomic Theory History
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Neils Bohr stated that electrons travel in a definite path around a nucleus. The electron paths are located in levels, certain distances from the nucleus. Electrons can jump from one level to the next, but cannot be in between levels.
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Chp. 4 Atomic Theory History Our current model of the atom is the result of much work between a number of different scientists.
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Chp. 4 Atomic Theory History Changes to the atomic theory include the following: Electrons do not travel in definite paths as Bohr claimed. Exact location of an electron cannot be determined, but scientists can say where the electron is likely to be, these are called electron clouds.
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Chp. 4 Atomic Theory History
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