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Atomic Structure Timeline

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Proposed that matter was composed of tiny indivisible particles ... Gold Foil Experiment. Discovered the nucleus. dense, positive charge in the center of the atom ... – PowerPoint PPT presentation

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Title: Atomic Structure Timeline


1
Atomic Structure Timeline
  • 4.1 Structure of the Atom
  • 4.3 Modern Atom

2
Democritus (400 B.C.)
  • Proposed that matter was composed of tiny
    indivisible particles
  • Believed atoms properties were based on shape
  • Greek atomos (indivisible)
  • Opposed by Aristotle who believed matter was
    infinite

3
John Dalton (1807)
  • British Schoolteacher
  • based his theory on experimental data
  • Billiard Ball Model
  • atom is a uniform, solid sphere

4
John Dalton
Daltons Theory
1. All elements are made of atoms. 2. Atoms of
the same element have the same mass. Atoms of
different elements have different
masses. 3. Compounds contain atoms of more than
one element. 4. In a particular compound, atoms
of different elements always combine in the same
way.
5
J. J. Thomson (1903)
  • Cathode Ray Tube Experiments
  • beam of negative particles
  • Discovered Electrons
  • negative particles within the atom
  • Plum-pudding Model

6
J. J. Thomson (1903)
  • Plum-pudding Model (a.k.a. Chocolate chip ice
    cream)
  • positive sphere (pudding) with negative
    electrons (plums) dispersed throughout

7
Ernest Rutherford (1911)
  • Gold Foil Experiment
  • Discovered the nucleus
  • dense, positive charge in the center of the atom
  • Nuclear Model

8
Ernest Rutherford (1911)
  • Nuclear Model
  • dense, positive nucleus surrounded by negative
    electrons

9
Niels Bohr (1913)
  • Bright-Line Spectrum
  • tried to explain presence of specific colors in
    hydrogens spectrum
  • Energy Levels
  • electrons can only exist in specific energy
    states
  • Planetary Model

10
Niels Bohr (1913)
Bright-line spectrum
  • Planetary Model
  • electrons move in circular orbits within specific
    energy levels

11
Erwin Schrödinger (1926)
  • Quantum mechanics
  • electrons can only exist in specified energy
    states
  • Electron cloud model
  • orbital region around the nucleus where e- are
    likely to be found

12
Erwin Schrödinger (1926)
  • Electron Cloud Model (orbital)
  • dots represent probability of finding an e- not
    actual electrons

13
James Chadwick (1932)
  • Discovered neutrons
  • neutral particles in the nucleus of an atom
  • Joliot-Curie Experiments
  • based his theory on their experimental evidence

14
James Chadwick (1932)
  • Neutron Model
  • revision of Rutherfords Nuclear Model
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