2_Lecture_BOHR_abbrev.pdf

2_Lecture_BOHR_abbrev.pdf - Structure of the atom What IS...

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Structure of the atom What IS the structure of an atom? What are the properties of atoms? REMEMBER: structure affects function! Important questions: Where are the electrons? What is the energy of an electron? Dual Nature of Light λν =c E = h ν Line Spectrum Bohr Model of Hydrogen Atom Chem 110 1 Photoelectric effect: light strikes a metal. If energy in is sufficient, an electron is ejected. Chem 110 2 Binding energy of the electron is the energy needed to remove it from the metal. The energy absorbed is converted to work w needed to remove the electron. w = work function (= binding energy of an electron to the metal. Classically: if we increase the energy (or amplitude) of wave (increase the number of photons), expect that eventually, there will be enough energy to pull the electron away from the metal. BUT: if frequency is low (below ν 0 ) NOTHING happens no matter how intense the beam.
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Photoelectric effect: Classically, expect metal to ± soak ² up energy of light until e binding energy ( w ) is overcome. BUT No e ³ s emitted until ν = ν 0 No waiting time Kinetic energy of e = h( ν ν 0 ) E k = ½ mv 2 where v = speed of electron emitted E photon = h( ν ν 0 ) = w + E k E k will increase as E photon increases Metal atoms absorb only 1 quantum of energy: it happens all at once as if struck by a particle ! photon Chem 110 3 Visible (white) light contains a continuous distribution of frequencies of electromagnetic radiation. Spectrum : distribution of ν in emitted radiation Chem 110 4
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Different types of light produce different spectra Examples Spectrum Type ν ’s Laser monochromatic one Light bulb continuous all Hg vapor discrete (or line) a few DEMONSTRATIONS: How can we explain all of this? Hg vapor spectrum Chem 110 5 Observation of line spectra implies that atoms have discrete (quantized) energy levels.
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