lecture 28 - Chapter 28 Atomic Physics Importance of...

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    Chapter 28 Atomic Physics
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    Importance of Hydrogen Atom Hydrogen is the simplest atom 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 This enables us to understand the periodic  table
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    More Reasons the Hydrogen  Atom is so Important The hydrogen atom is an ideal system for  performing precise comparisons of theory  with experiment Also for improving our understanding of atomic  structure Much of what we know about the hydrogen  atom can be extended to other single-electron  ions  For example, He +  and Li 2+
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    Sir Joseph John Thomson “J. J.” Thomson 1856  - 1940 Discovered the electron Did extensive work with  cathode ray deflections 1906 Nobel Prize for  discovery of electron
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    Early Models of the Atom J.J. Thomson’s model  of the atom A volume of positive  charge Electrons embedded  throughout the volume A change from  Newton’s model of the  atom as a tiny, hard,  indestructible sphere
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    Early Models of the Atom, 2 Rutherford, 1911 Planetary model Based on results of thin  foil experiments Positive charge is  concentrated in the  center of the atom, called  the  nucleus Electrons orbit the  nucleus like planets orbit  the sun
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    Scattering Experiments The source was a naturally radioactive material that  produced alpha particles Most of the alpha particles passed though the foil A few deflected from their original paths Some even reversed their direction of travel
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    Difficulties with the Rutherford  Model Atoms emit certain discrete characteristic  frequencies of electromagnetic radiation The Rutherford model is unable to explain this phenomena Rutherford’s electrons are undergoing a  centripetal acceleration and so should radiate  electromagnetic waves of the same frequency The radius should steadily decrease as this radiation is  given off The electron should eventually spiral into the nucleus, but it  doesn’t
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    Emission Spectra A gas at low pressure has a voltage applied to it A gas emits light characteristic of the gas When the emitted light is analyzed with a  spectrometer, a series of discrete bright lines is  observed Each line has a different wavelength and color This series of lines is called an  emission spectrum
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    Examples of Emission Spectra
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    Emission Spectrum of  Hydrogen – Equation  The wavelengths of hydrogen’s spectral lines  can be found from R H  is the  Rydberg constant R H  = 1.097 373 2 x 10
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lecture 28 - Chapter 28 Atomic Physics Importance of...

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