The Atomic Model

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The Atomic Model

• Chem 9

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The Greek Model

• Democritus - A Greek Philosopher, 400 BC.
• Concluded that matter could not be divided into
  smaller and smaller pieces forever.
• Eventually, the smallest piece of matter would be
  found.
• He used the word "Atomos meaning indivisible.

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The Dalton Model Billiard Ball Model

• John Dalton - The English chemist that proposed
• first Atomic Theory in 1803.
• All elements are composed of indivisible
  particles.
• Atoms of the same element are exactly alike.
• Atoms of different elements are different.
• Compounds are formed by joining atoms of two or
  more elements

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The Thomson Model Chocolate Chip Cookie
ModelPlum Pudding Model

• J. J. Thomson 1856 1940 (English scientist)
• discovered negative particle (an Electron) in
  1887
• by using a cathode ray tube
• initially called electrons CORPUSLES

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Robert A. Millikan (1868 1953)

• 1900 mass of Electron approximately 1/2000 the
  mass of a Hydrogen atom
• 1916 -determined the charge carried by an
  electron
• Millikan OIL DROP EXPERIMENT

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Eugene Goldstein (1850 -1930)

• 1866 Eugene Goldstein found Positive particle
  Protons
• He named them CANAL RAYS

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Sir James Chadwick 1891 - 1974

• Discovered
• the neutron in 1932
• Has no charge
• Neutrons mass is close to protons mass

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Ernest Rutherford - British Physicist Gold Foil
Experiment

• In 1908, proved the atom had a small,
• dense, positively charged Nucleus.
• He said an atom is mostly empty space and
• negative electrons are scattered around
• the outside edge.

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Niels Bohr (Danish scientist)The Planetary
Model - 1913

• Bohr proposed
• Electrons move in definite orbits around the
  nucleus, like planets moving around the sun.
• That each electron moves in a specific energy
  level.

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Quantum Mechanical Model

• Erwin Schrodinger (1887-1961)
• -Electrons have NO definite path in an atom.
• -Only a probable location is known based
• on how much energy it has.
• -Atomic orbitals (s,p,d,f) are NOT fixed paths
  as Bohr suggested

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Summary

• Dalton Solid Sphere
• Thomson Pos. neg mixed together
• Rutherford Positive nucleus, neg electrons
  surrounding it
• Bohr Positive nucleus, neg electrons in exact
  orbits
• Quantum Mechanical Theory
• (Electron cloud theory)