The Bohr Model of the Atom

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Chapter 4

• The Bohr Model of the Atom

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Visible Light
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Niels Bohr

• In 1913 Bohr published a theory about the
  structure of the atom based on an earlier theory
  of Rutherford's.
• Bohr expanded upon this theory by proposing that
  electrons travel only in certain successively
  larger orbits.

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Bohr Model of the Atom

• Electrons orbit the nucleus in orbits that
  represent specific quantities of energy.
• The energies of the electrons in the atom are
  quantized.
• Only certain electron orbits (energy levels) are
  allowed.

The Bohr Atom
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Niels Bohr

• Bohr also described the way atoms emit radiation
  by suggesting that when an electron jumps from an
  outer orbit to an inner one, that it emits light.

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Ground State

• The lowest energy state of an atom.

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Excited State

• Any energy state of an atom that is higher in
  energy than the ground state.

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Energy Absorbed
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Absorption (Dark Line) Spectra
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Energy Emitted
Electron jumps to a lower orbit
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Emission (Bright Line) Spectra
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Emission Spectra
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The lines present in an emission spectrum are the
lines missing in an absorption spectrum.
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Demonstration

• Diffraction Grating and White Light
• Gas Tubes (He, Hg, Ne) and Diffraction Grating

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Describe the process that occurs inside atoms
that produces the spectra?

• Energy is absorbed by the atom.
• The electrons jump into higher orbits and the
  atom becomes excited.
• The electrons return to their original orbits and
  the atom returns to the ground state.
• The electrons release energy in the form of
  visible light.
• The specific energies (wavelengths, frequencies)
  of visible light absorbed and released produce
  the spectra.

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Homework

• Chapter 4 Worksheet 2 (due tomorrow).
• Lab Summary Flame Tests (due Thursday).
• Study Guide Chapter 4 (due Friday).