The Development of Atomic Models

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The Development of Atomic Models

• Democritus was a pre-Socratic Greek philosopher
  (born around 460 BC).
• Democritus was originator of the belief that all
  matter is made up of various imperishable,
  indivisible elements which he called "atomos",
  from which we get the English word atom.

• According to legend, Democritus was supposed to
  be mad because he laughed at everything, and so
  he was sent to Hippocrates to be cured.
  Hippocrates pointed out that he was not mad, but,
  instead, had a happy disposition. That is why
  Democritus is sometimes called the laughing
  philosopher.

BB - Model Daltons Model More to come
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Plum Pudding Model
Thomson's model was compared (though not by
Thomson) to a British treat called plum pudding,
hence the name. It has also been called the
chocolate chip cookie model, but only by those
who have not read Thomson's original paper

• Proposed by J. J. Thomson (1856 - 1940), the
  discoverer of the electron in 1897.
• The plum pudding model was proposed in March,
  1904 before the discovery of the atomic nucleus.
• In this model, the atom is composed of electrons
  surrounded by a soup of positive charge to
  balance the electron's negative charge, like
  plums surrounded by pudding. The electrons were
  thought to be positioned throughout the atom.
• Electrons could move like letters in alphabet
  soup
• Instead of a soup, the atom was also sometimes
  said to have had a cloud of positive charge.

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Nuclear Model

• The Gold foil experiment or the Rutherford
  experiment was an experiment done by Ernest
  Rutherford (1871 - 1937) in 1909. This experiment
  discovered the nucleus.
• Led to the downfall of the plum pudding model of
  the atom.
• Alpha particles (positive particles--Helium
  Nuclei) were shot at gold foil.
• Particles passed through the gold foil. A few
  shot back.
• Conclusions

1. Atom is mostly empty space 2. Dense center
called the nucleus 3. Electrons were stuck
surrounding the nucleus.
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Planetary Model

• Introduced by Niels Bohr, a Danish physicist
  (1885 - 1962), in 1913.
• Because of its simplicity, the Bohr model is
  still commonly taught to introduce students to
  quantum mechanics.
• The Bohr model depicts the atom as a small,
  positively charged nucleus surrounded by waves of
  electrons in orbit similar in structure to the
  solar system, but with electrostatic forces
  providing attraction, rather than gravity.

"The opposite of a correct statement is a false
statement. But the opposite of a profound truth
may well be another profound truth." Niels Bohr
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Quantum Mechanical Model

• Erwin Schrödinger (August 12, 1887 January 4,
  1961)
• An Austrian physicist, achieved fame for his
  contributions to quantum mechanics, especially
  the Schrödinger equation, for which he received
  the Nobel Prize in 1933.
• This model is based on probability
• Where are you going to find and electron 90 of
  the time.
• Atom is viewed as a fuzzy cloud.
• Schrödinger equations create electron clouds
  (orbitals) with specific shapes.

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Main Points For Atoms Video

• What is the key to understanding atomic
  structure?
• The discovery of what particle is associated with
  the Crooks Tube?
• What did Rutherford expect to happen in the gold
  foil experiment?
• What was Rutherfords genius?
• What conclusions did Rutherford draw from the
  Gold foil experiment?
• How much smaller is the nucleus than the electron
  cloud?
• What determines the shape of the electron cloud?