chapter28 - Chapter 28 Atomic Physics Sir Joseph John...

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Chapter 28 Atomic Physics
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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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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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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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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 7 m -1 n is an integer, n = 1, 2, 3, … The spectral lines correspond to different values of n 2 2 H n 1 2 1 R 1
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Spectral Lines of Hydrogen The Balmer Series has lines whose wavelengths are given by the preceding equation Examples of spectral lines n = 3, λ = 656.3 nm n = 4, λ = 486.1 nm
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Other Series Lyman series Far ultraviolet Ends at energy level 1 Paschen series Infrared (longer than Balmer) Ends at energy level 3
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General Rydberg Equation The Rydberg equation can apply to any series m and n are positive integers n > m H R λ mn 22 1 1 1
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Absorption Spectra An element can also absorb light at specific wavelengths An absorption spectrum can be obtained by passing a continuous radiation spectrum through a vapor of the gas The absorption spectrum consists of a series of dark lines superimposed on the otherwise continuous spectrum The dark lines of the absorption spectrum coincide with the bright lines of the emission spectrum
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Absorption Spectrum of Hydrogen
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Applications of Absorption Spectrum
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chapter28 - Chapter 28 Atomic Physics Sir Joseph John...

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