HONR228Q Notes section g:

  • Atomic and Molecular Spectra

    1. Electron Transitions and Atomic Spectra

      1. The Hydrogen Atom
        1. Atomic States
          1. Slide showing scaled energy level structure of hydrogen atom
          2. Energy levels labeled by quantum number n = 1, 2, 3, 4, etc.
          3. States of electrons form "standing waves"
          4. Binding energy is En=-13.6Z2/n2 eV
        2. Transitions and Spectrum
          1. Natural (stable) state is lowest energy state
          2. Raise energy level or state by adding energy to electron
          3. Electron emits photon when it drops from higher to lower energy level
          4. Transition "series" for the hydrogen atom:
            • N=2, 3, 4, etc. down to N=1: Lyman series (ultraviolet)
            • N=3, 4, 5, etc. down to N=2: Balmer series (first three visible)
            • N=4, 5, 6, etc. down to N=3: Paschen series (infrared)
      2. Multi-electron Atoms
        1. Model:
          1. DEMO P3-53: ATOMIC ENERGY LEVEL MODEL
          2. Illustrates aspects of atomic structure and transitions in multi-electron atoms
        2. Structure
          1. Electrons fill states beginning with lowest energy level
          2. Natural state has lowest energy
          3. Due to shielding by other electrons, last electron acts like single-electron atom
          4. All atoms approximately same size: ~10-10 meters
        3. Transitions
          1. Transitions involve single electron
          2. Generally least strongly bound electron

    2. Atomic and Molecular Spectra

      1. Spectrum of white light
        1. Experiments
          1. DEMO N1-01: PRISMATIC SPECTRUM OF WHITE LIGHT - POINT SOURCE
          2. DEMO N1-11: DIFFRACTION SPECTRUM OF WHITE LIGHT - POINT SOURCE
        2. Observations
          1. Fundamental examples of continuous spectrum
          2. Physical process called "dispersion" of light
          3. Separates light by wavelength or frequency
          4. Blue bends most in prism, red bends most in grating
      2. Hydrogen spectrum and its source
        1. Demonstrations and References
          1. DEMO P3-51: BALMER SERIES
          2. Slide showing scaled energy level structure of hydrogen atom
        2. Observations and conclusions
          1. Several "series" of transition lines present
            • Balmer series to n=2 is visible:
              • Red is n=3 to n=2
              • Cyan is n=4 to n=2
              • Blue is n=5 to n=2
            • Lyman series to n=1 is UV
            • Paschen series to n=3 is IR
          2. Calculate energies/frequencies/wavelengths of Balmer lines
      3. Atomic spectra
        1. Spectra of Gas Discharges for the light elements. NICE!
        2. DEMO N2-02: DIFFRACTION SPECTRA - 3 SOURCES - EXPENDABLE GRATINGS
          1. Demonstrates differences between two atomic spectra
          2. Hg and Cd Spectra
          3. Different series of lines due to different energy level configuration for outer electron
          4. Unique spectrum for each individual atom
        3. DEMO N2-03: DIFFRACTION SPECTRUM OF SODIUM - EXPENDABLE GRATINGS
          1. High-pressure sodium lamp spectrum
          2. Mercury added for more efficient starting
          3. Note bright yellow line (actually doublet) with other lines
          4. As it heats collision broadening leads to more continuous spectrum
          5. After bulb hot dark line develops in center of yellow
          6. Demonstrates line spectrum and absorption spectrum
          7. Analog to discovery of helium on the sun
      4. Molecular spectra
        1. Experiment
          1. DEMO N2-05: DIFFRACTION SPECTRA - MISCELLANEOUS TUBES
          2. DEMO P3-24: CATHODE-RAY TUBES - MISCELLANEOUS
        2. Conclusions
          1. Large variation in spectral configuration
          2. Atomic spectra have widely and irregularly spaced lines or groups of lines
          3. Molecular spectra have uniformly spaced groups of lines
          4. Each atomic or molecular spectrum is unique, due to unique electron or molecule configuration

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