Ch28 - Chapter 28 PHY213 1 Chapter 28 Atomic Physics...

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Unformatted text preview: Chapter 28 PHY213 1 Chapter 28 Atomic Physics Importance of Hydrogen Atom s Hydrogen is the simplest atom s The quantum numbers used to characterize the allowed states of hydrogen can also be used to describe (approximately) the allowed states of more complex atoms s This enables us to understand the periodic table More Reasons the Hydrogen Atom is so Important s The hydrogen atom is an ideal system for performing precise comparisons of theory with experiment s Also for improving our understanding of atomic structure s Much of what we know about the hydrogen atom can be extended to other single-electron ions s For example, He + and Li 2+ Sir Joseph John Thomson s J. J. Thomson s 1856 - 1940 s Discovered the electron s Did extensive work with cathode ray deflections s 1906 Nobel Prize for discovery of electron Chapter 28 PHY213 2 Early Models of the Atom s J.J. Thomsons model of the atom s A volume of positive charge s Electrons embedded throughout the volume s A change from Newtons model of the atom as a tiny, hard, indestructible sphere Early Models of the Atom, 2 s Rutherford, 1911 s Planetary model s Based on results of thin foil experiments s Positive charge is concentrated in the center of the atom, called the nucleus s Electrons orbit the nucleus like planets orbit the sun Scattering Experiments s The source was a naturally radioactive material that produced alpha particles s Most of the alpha particles passed though the foil s A few deflected from their original paths s Some even reversed their direction of travel Difficulties with the Rutherford Model s Atoms emit certain discrete characteristic frequencies of electromagnetic radiation s The Rutherford model is unable to explain this phenomena s Rutherfords electrons are undergoing a centripetal acceleration and so should radiate electromagnetic waves of the same frequency s The radius should steadily decrease as this radiation is given off s The electron should eventually spiral into the nucleus, but it doesnt Chapter 28 PHY213 3 Emission Spectra s A gas at low pressure has a voltage applied to it s A gas emits light characteristic of the gas s When the emitted light is analyzed with a spectrometer, a series of discrete bright lines is observed s Each line has a different wavelength and color s This series of lines is called an emission spectrum Emission Spectrum of Hydrogen Equation s The wavelengths of hydrogens spectral lines can be found from s R H is the Rydberg constant s R H = 1.097 373 2 x 10 7 m-1 s n is an integer, n = 1, 2, 3, s The spectral lines correspond to different values of n...
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Ch28 - Chapter 28 PHY213 1 Chapter 28 Atomic Physics...

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