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In 340 BC, Aristotle disagreed with Democritus theory of atoms. He believed that you would end up with a particle that could not be cut. Aristotle believed that matter is made of Earth, fire, air, and water.
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400 BC
Proposed that small particles called Atoms make up all matter. -
He published his atomic theory. His theory states: All substances are made of atoms. They are small particles that cannot be created, divided, or destroyed. Atoms of the same element are exactly alike, & atoms of different elements are different. Atoms join with other atoms to make new substances.
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Revised Atomic Theory
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Developed the first periodic table of elements.
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Identifies electrons as particles that are present in every atom. Plum-pudding Model.
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He discovery that most of an atom's mass is located in a dense region now called the nucleus.
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This model suggested that most of the mass of the atom was contained in the small nucleus, and that the rest of the atom was mostly empty space.
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Bohr model of the atom
This model shows that electrons are in energy levels. -
He determined the number of protons in an atom. This is called the Atomic number.
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They created the Electron Cloud Model.
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He discovered the neutron, one of the particles in the nucleus of an atom.
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He devised the Modern Periodic Table.
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They developed a scanning tunneling microscope, which is used to see atoms for the first time.
