chem 447 Chapters 8-10 notes

chem 447 Chapters 8-10 notes - Chapter 8 (based on...

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Chapter 8 (based on importance; problems assigned, lecture notes, extra book notes) Based on problems: (#1, 4, 9) possible answers? 1. Molecular bands and continuum radiation are a potential source of interference that must be minimized by proper choice of wavelength , by background correction, or by a change in atomization conditions. 4. The uncertainty effect, usually 10^-4 angstroms 9. Boltzmann Distribution Optical Spec – elements converted to gaseous atoms or elementary ions by atomization The entire scale of an energy diagram is the ionization energy of the lowest occupied valence orbital. P.215 p-orbitals differ in energy very slightly – difference is due to electrons either spinning on an axis in the same direction as its orbital motion or opposite to its orbital motion. Spin and orbital motions both create magnetic fields: -Fields interact attractively if these two motions are in opposite directions, and vice versa; as a result the energy of the electron with spin opposing orbital motion is slightly lower…. -similar differences in d and f orbitals as above. -For most atoms having 1 valence electron (Mg+, Al2+, uncharged alkali metals), the energy diagram has same general appearance, however energy differences are different with each Singlet-to-triplet transition (AKA excited electron spin is parallel to unexcited electron —“upaired” see p.217) is less favorable than singlet-to-singlet transition. -Energy diagrams: thick lines = most probable transitions, faint lines = forbidden (less probable) transitions Atomic Emission Spectra: -Ways to excite electron: heat of a flame, plasma, electric arc or spark -Excited atom has brief lifetime and returns to ground state resulting in photon emission Atomic absorption spectra: consistent predominantly of resonance lines, which are the result of transitions from the ground state to upper levels. Atomic Fluorescence Spectra Measured at 90 degrees to the light path Observe resonance fluorescence involving transitions from excited states returning to ground states Two types of returning to ground state: 1. Resonance fluorescence (normal) 2. Fluorescence emission followed by a radiationless deactivation to ground state Atomic Line Width Line width is measured as Δλ 1/2 Four sources of line broadening (from book): 1. The uncertainty effect 2. The Doppler effect 3. Pressure effects due to collisions between atoms of the same kind and with foreign atoms 4. Electric and magnetic field effects (in chapter 9) Another source of line broadening is temperature (from lecture). The Uncertainty Effect
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Δv·Δt ≥ 1 Line widths due to uncertainty broadening are sometimes called natural line widths The Doppler Effect (Doppler Broadening) Approx two orders of magnitude greater than the natural line width Photons move away from transducer – frequency decreases, red shift Photons toward the transducer – frequency increases, blue shift When atom moves toward photon detector and emits radiation, detector sees wave crests more often and
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chem 447 Chapters 8-10 notes - Chapter 8 (based on...

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