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CHAPTER 5 The Structure of the Atom 5.4 Light and Spectroscopy
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2 Today 1808 1870 189719101925 Democritus Atomism 460 – 370 BC Dalton “Modern” atomic theory Crookes Cathode rays Thomson Discovery of the electron Rutherford Discovery of the nucleus Pauli Pauli exclusion principle
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3 5.4 Light and Spectroscopy Today 1808 1870 189719101925 Democritus Atomism 460 – 370 BC Dalton “Modern” atomic theory Crookes Cathode rays Thomson Discovery of the electron Rutherford Discovery of the nucleus Pauli Pauli exclusion principle
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4 5.4 Light and Spectroscopy Today 1808 1870 18971910 Democritus Atomism 460 – 370 BC Dalton “Modern” atomic theory Crookes Cathode rays Thomson Discovery of the electron Rutherford Discovery of the nucleus 1925 Pauli Pauli exclusion principle
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5 5.4 Light and Spectroscopy Today 1808 1870 18971910 Democritus Atomism 460 – 370 BC Dalton “Modern” atomic theory Crookes Cathode rays Thomson Discovery of the electron Rutherford Discovery of the nucleus 1925 Pauli Pauli exclusion principle Do we have evidence to support these claims?
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6 5.4 Light and Spectroscopy Light is a form of electromagnetic energy that comes from electrons in atoms The human eye can only detect a certain range of that energy: the visible spectrum.
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7 5.4 Light and Spectroscopy Light is a form of electromagnetic energy that comes from electrons in atoms The human eye can only detect a certain range of that energy: the visible spectrum.
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8 5.4 Light and Spectroscopy White light from a lamp or the sun is not truly white! Analyzing starlight with a prism (one of the first spectrometers)
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9 5.4 Light and Spectroscopy Visible light is only a small range in the electromagnetic spectrum
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10 5.4 Light and Spectroscopy We are surrounded by electromagnetic energy
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11 5.4 Light and Spectroscopy Remember that light travels as bundles called photons 1 electron volt (eV) = 1.602 x 10 –19 J. A very small unit of energy Energy of a photon
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12 5.4 Light and Spectroscopy Wavelength and frequency are related
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13 5.4 Light and Spectroscopy The wavelength of red laser light is 652 nm. What is its frequency? How much energy does a photon of this light have in electron volts?
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14 5.4 Light and Spectroscopy The wavelength of red laser light is 652 nm. What is its frequency? How much energy does a photon of this light have in electron volts? Asked:Frequency and energy Given: Relationships:
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15 5.4 Light and Spectroscopy The wavelength of red laser light is 652 nm. What is its frequency? How much energy does a photon of this light have in electron volts? Asked:Frequency and energy Given: Relationships: Solve:
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16 5.4 Light and Spectroscopy The wavelength of red laser light is 652 nm. What is its frequency? How much energy does a photon of this light have in electron volts? Asked:Frequency and energy Given: Relationships: Solve:
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17 5.4 Light and Spectroscopy The wavelength of red laser light is 652 nm. What is its frequency? How much energy does a photon of this light have in electron volts? Asked:Frequency and energy Given: Relationships: Solve: Answer:Since 1 Hz = 1/s, the frequency is 4.6 x 10 14 Hz and the energy is 1.9 eV.
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18 5.4 Light and Spectroscopy prism electron all possible energy levels Light from an incandescent light bulb:
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19 5.4 Light and Spectroscopy prism electron fixed energy levels Light from pure hydrogen:
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20 5.4 Light and Spectroscopy Hydrogen atoms can only absorb and emit light of very specific energies.
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21 5.4 Light and Spectroscopy Why does the atom absorb only specific (discrete) energies? Matter and light
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22 5.4 Light and Spectroscopy Remember: only some energy levels are allowed. Why does the atom absorb only specific (discrete) energies? Matter and light
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23 5.4 Light and Spectroscopy Energy levels Photon (energy) Energy levels Energy of the photon matches a gap between levels Energy (light) is absorbed. Energy of the photon does not match a gap between levels Energy (light) passes through the atom. Matter and light
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24 5.4 Light and Spectroscopy Energy levels Photon (energy) Energy of the photon matches a gap between levels Energy (light) is absorbed. another photon is emitted specific color (wavelength) Matter and light
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25 5.4 Light and Spectroscopy Each type of atom has a different electron structure. Each element has unique energy levels like a fingerprint.
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26 5.4 Light and Spectroscopy Spectrum cards How to read the spectrum cards
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27 5.4 Light and Spectroscopy Combinations of elements contain spectral lines from both. Spectrum cards
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28 5.4 Light and Spectroscopy Photon emitted Photon absorbed Energy levels Photon (energy) Energy of the photon matches a gap between levels Reemission of light has two steps:
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29 5.4 Light and Spectroscopy Energy levels Photon (energy) Range of energies Emission spectrum Absorption spectrum
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30 5.4 Light and Spectroscopy Visible light is only a small range of the electromagnetic spectrum.
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31 5.4 Light and Spectroscopy Each type of atom has a different electron structure. Each element has unique energy levels like a fingerprint.
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