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lecture_11 - 4.1 The Atomic Models of Thomson and...

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Unformatted text preview: 4.1 The Atomic Models of Thomson and Rutherford 4.2 Rutherford Scattering 4.3 The Classic Atomic Model 4.4 The Bohr Model of the Hydrogen Atom 4.5 Successes and Failures of the Bohr Model 4.6 Characteristic X-Ray Spectra and Atomic Number 4.7 Atomic Excitation by Electrons CHAPTER 4 Structure of the Atom Structure of the Atom In the present first part of the paper the mechanism of the binding of electrons by a positive nucleus is discussed in relation to Plancks theory. It will be shown that it is possible from the point of view taken to account in a simple way for the law of the line spectrum of hydrogen.- Niels Bohr, 1913 Structure of the Atom Pieces of evidence that scientists had in 1900 to indicate that the atom was not a fundamental unit: 1) There seemed to be too many kinds of atoms, each belonging to a distinct chemical element. 2) Atoms and electromagnetic phenomena were intimately related. 3) The problem of valence . Certain elements combine with some elements but not with others, a characteristic that hinted at an internal atomic structure. 4) The discoveries of radioactivity, of x rays, and of the electron. Thomsons plum-pudding model of the atom had the positive charges spread uniformly throughout a sphere the size of the atom, with electrons embedded in the uniform background. In Thomsons view, when the atom was heated, the electrons could vibrate about their equilibrium positions, thus producing electromagnetic radiation. Thomsons Atomic Model Experiments of Geiger and Marsden Rutherford, Geiger, and Marsden conceived a new technique for investigating the structure of matter by scattering particles from atoms. Geiger showed that many particles were scattered from thin gold-leaf targets at backward angles greater than 90. Example 4.1 The maximum scattering angle corresponding to the maximum momentum change. Maximum momentum change of the -particle is or Determine by letting p max be perpendicular to the direction of motion. If an particle were scattered by many electrons and N electrons results in . The number of atoms across the thin gold layer of 6 10-7 m: Assume the distance between atoms is and there are . That gives . Multiple Scattering from Electrons if the particle scattered from all 79 electrons in each atom of gold. The experimental results were not consistent with Thomsons atomic model. Rutherford proposed that an atom has a positively charged core (nucleus) surrounded by the negative electrons. Rutherfords Atomic Model Scattering experiments help us study matter too small to be observed directly....
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This note was uploaded on 04/15/2008 for the course PHY 361 taught by Professor Alarcon during the Spring '08 term at ASU.

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lecture_11 - 4.1 The Atomic Models of Thomson and...

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