Physics 27: 7-13 The Bohr Atom
Text Reading: Giancoli, Physics - Principles with Applications, Chapter 27: Sections 7 to 13
- 27: 7 In order to resolve the apparent contradiction implied by light's apparent wavelike antiparticle like behavior, Niels Bohr proposed the principle of complementarity, which suggests that both views are necessary to completely understand light phenomena.
- 27: 8 Louis de Broglie extended this principle to all matter. The corresponding wavelength of most ordinary objects is too small to be detected; the wave nature of monitor can only be directly perceived when particles on the atomic or subatomic scale.
- 27: 9 Electron transmission microscopes and electron scanning microscopes both developed when electrons were perceived to have wavelike properties.
- 27: 10 In the early 19th century, Dalton found a chemistry on the principle that an atom was in single, indivisible particle of matter with particular chemical properties. The Curies' studies of radioactivity and J. J. Thomson's discovery that beta rays consisted of particles with masses smaller than that of hydrogen atoms suggested that atoms consisted of several small subatomic particles. Rutherford's experiment, in which he directed alpha particles at a thin sheet of gold metal foil and tracked their ricochet pattern, led to the planetary model: a very small, concentrated nucleus containing all positive charge, surrounded by electrons constantly in motion with different energy levels.
- 27: 11 The combination of quantum mechanics and Rutherford's experiments allowed physicists to map emitted energy in the form of line spectra to electron shifts from energy level to another. Ballmer's experiments led to the discovery of the Rydberg constant and a way to predict spectral lines as a result of electron energy level changes for hydrogen.
- 27: 12 In Bohr's model of the atom, the energy level or energy state of an electron depends on its distance from the nucleus, and the positive charge on the nucleus. Bohr also proposed that quantum theory should predict classical results for the macroscopic world (the correspondence principle).
- 27: 13 Bohr was unable to explain why orbits should be quantized. However, de Broglie's theory of wave-particle duality requires that electrons produce a standing wave across their orbitals so that destructive interference cannot take place.
|De Broglie Wavelength
||Objects with momentum m will have an associated wavelength of λ.
|Rydberg Constant Equation
||The wavelength of light emitted when an electron changes orbitals is a function of the energy levels of the initial and final orbital.
||The radius of the nth orbital of an atom with atomic number Z (i.e., Z protons) is rn.
||Energy of an electron
||This gives the energy of an electron in energy level n of an atom with Z protons.
Read the following weblecture before chat: The Bohr Atom
Use the Bohr Model Simulator at the McGraw-Hill education site.
- Read the Introduction and How To tabs so that you understand the theory of the Bohr atom and the operation of the simulator.
- Carry out the exercises on the exercise tab and check your solutions.
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