Physics 27: 7-13 The Bohr Atom
Homework
Reading Preparation
Text Reading: Giancoli, Physics - Principles with Applications, Chapter 27: Sections 7 to 13
Study Points
- 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.
Key Equations
De Broglie Wavelength |
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Objects with momentum m will have an associated wavelength of λ. |
Rydberg Constant Equation |
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The wavelength of light emitted when an electron changes orbitals is a function of the energy levels of the initial and final orbital. |
Orbital radius |
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The radius of the nth orbital of an atom with atomic number Z (i.e., Z protons) is rn. |
Energy of an electron |
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This gives the energy of an electron in energy level n of an atom with Z protons. |
Web Lecture
Read the following weblecture before chat: The Bohr Atom
Study Activity
Use the Bohr Model Simulator at PhET to explore the characterstics of the atom.
- How does light interact with electrons?
- How does the wavelength of the light affect the energy state of the electron that absorbs it? of the electron that emits it?
Chat Preparation Activities
- Forum question: The Moodle forum for the session will assign a specific study question for you to prepare for chat. You need to read this question and post your answer before chat starts for this session.
- Mastery Exercise: The Moodle Mastery exercise for the chapter will contain sections related to our chat topic. Try to complete these before the chat starts, so that you can ask questions.
Chapter Quiz
- Required: Complete the Mastery exercise with a passing score of 85% or better.
- Go to the Moodle and take the quiz for this chat session to see how much you already know about astronomy!
Lab Work
If you want lab credit for this course, you must complete at least 18 labs; you may complete more if you are preparing for the AP exam.. One or more lab exercises are posted for each chapter as part of the homework assignment. We will be reviewing lab work at regular intervals, so do not get behind!
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