Atomic Structure Timeline - Use the following information to fill out your foldable. You will be responsible for the information found on this ...

Atomic Structure Timeline

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Democritus (400 B.C.)

          • Proposed that matter was
            composed of tiny indivisible
            particles

          • Not based on experimental
            data

          • Greek: atomos

Alchemy (next 2000 years)
• Mixture of science and mysticism.
• Lab procedures were developed, but alchemists did not
  perform controlled experiments like true scientists.

John Dalton (1807)

         • British Schoolteacher
           – based his theory on others’
             experimental data

         • Billiard Ball Model
           – atom is a
             uniform,
             solid sphere

John Dalton
         Dalton’s Four Postulates
1. Elements are composed of small indivisible
   particles called atoms.
2. Atoms of the same element are identical.
   Atoms of different elements are different.
3. Atoms of different elements combine together
   in simple proportions to create a compound.
4. In a chemical reaction, atoms are rearranged,
   but not changed.

Henri Becquerel (1896)

          • Discovered radioactivity
            – spontaneous emission of
              radiation from the nucleus
          • Three types:
            – alpha () - positive
            – beta () - negative
            – gamma () - neutral

J. J. Thomson (1903)

          • Cathode Ray Tube
            Experiments
            – beam of negative particles

          • Discovered Electrons
            – negative particles within
              the atom

          • Plum-pudding Model

J. J. Thomson (1903)

             Plum-pudding Model
               – positive sphere
                 (pudding) with
                 negative electrons
                 (plums) dispersed
                 throughout

Ernest Rutherford (1911)

          • Gold Foil Experiment
          • Discovered the nucleus
            – dense, positive charge in
              the center of the atom

          • Nuclear Model

Ernest Rutherford (1911)

  • Nuclear Model
    – dense, positive nucleus surrounded
      by negative electrons

Niels Bohr (1913)

           • Bright-Line Spectrum
             – tried to explain presence
               of specific colors in
               hydrogen’s spectrum

           • Energy Levels
             – electrons can only exist in
               specific energy states

           • Planetary Model

Niels Bohr (1913)

       Bright-line spectrum

            • Planetary Model
              – electrons move in circular
                orbits within specific
                energy levels

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

Erwin Schrödinger (1926)

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

James Chadwick (1932)

         • Discovered neutrons
           – neutral particles in the
             nucleus of an atom

         • Joliot-Curie
           Experiments
           – based his theory on their
             experimental evidence

James Chadwick (1932)

            Neutron Model
 • revision of Rutherford’s Nuclear Model

1964
     Murray Gell-Mann & George Zweig

Murray Gell- Mann was an American physicist who received a Nobel Prize for his
theory on elementary particles. He also found that all the elements of an atom are held
together by quarks. To find this, he blasted high speed electrons into a hydrogen atom.
George Zweig proposed the existence of quarks. He thought of them as aces, because he
guessed there were four quarks in every atom.
Now, in the same year, both these guys proposed the idea of quarks. They tested
electrical charges, and that how the numbers for quarks came about.

http://www.profes.net/rep_imagenes/Monograf/NF1990a.jpg
http://panda.unm.edu/images/people/faculty/gell_mann_murray.jpg

History of the Atom - Timeline
                                     Antoine Lavoisier
                                    makesJ.J.  Thomson
                                           a substantial        Niels Bohr
                                  number discovers    the
                                         of contributions       proposes
                                          electron
                                      to the         and
                                              field of                                James
                                                                the Bohr             Chadwick
                                         proposes the
                                        Chemistry                Model in          discovered
                                         Plum Pudding
                    1766 – 1844                                    1913            the neutron
                                         Model 1871
                                                 in 1897
                                                       – 1937
                                                                     1887 – 1961    in in 1932
  460 – 370 BC

                                              1700s
                                              1800s
                                              1900s
             0

                                                                         Erwin
 Democritus                              John DaltonErnest RutherfordSchrodinger
  proposes                               proposes performs
                                                  his      the Gold Foil
                                                                      describes
the 1st atomic                         atomic theory
                                                   Experiment
                                                      in       in 1909
                                                                     the electron
                                                                             1891 – 1974

   theory         1743 – 1794               1803                    cloud in 1926

                                                            1885 – 1962

                                        1856 – 1940

Progression of the Atomic Model

                               -
                                -      -
                       -        -
                                - -
                           -   --+-
                                 -    +- -   Electron Cloud

                       -        -
                                -
                                -

The structure of an atom, according to:      Democritus
                                           James
                                           Ernest
                                           Erwin
                                              Neils
                                            J.J.    Bohr&
                                                 Schrodinger
                                                  Chadwick
                                                  Rutherford
                                                  Thomson
                                             John Dalton