Transcript Energy levels, photons and spectral lines

Quantum Physics
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Quantum
The smallest quantity of a substance that still has the
specific properties of that substance
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• Discrete vs. Continuous
Albert Einstein showed that light is quantized and
contains photons
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• Packets of energy
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Quantum Physics
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Balmer Series
How did physicists determine that the energy levels of
electrons are quantized?
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Isaac Newton – prism and sunlight → light is a wave
Interference patterns like with water → light is a wave
Joseph von Fraunhofer – the Sun’s spectrum has gaps → ?
Observations of gas emission and absorption spectrum → ?
J. J. Balmer develops an equation that analyzes the
pattern on the spectral lines that are observed.
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Quantum Physics
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Quantum Physics
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Photons
Max Planck showed how the radiation emitted or
absorbed by an object was quantized but still thought of
light as a wave.
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• Einstein showed that photons have energy E = hf
• Confirmed though experimentation by Robert Millikan
Since h = 6.63 x 10-34 Js, each photon carries a very
small amount of energy
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Quantum Physics
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Photoelectric Effect
Shining light on metal could cause electrons to be
ejected from the metal.
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• This could not be explained using the wave theory of light
Einstein’s photon theory of light explained the
observations concerning the ejection of electrons from
metals.
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• Waves vs. Photons
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Quantum Physics
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The Bohr atom
Thomson, Rutherford and Millikan discover the
structure of the atom
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Classical EM theory could not explain this structure
Niels Bohr developed a model of the atom where the
electrons had certain stable states that had quantized
radii and energy
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• Bound states of the electron in hydrogen
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Quantum Physics
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Energy levels, photons and spectral lines
Bohr’s model of the atom matches the observations of
spectral lines from hydrogen
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• “Jumping” of the electron between energy levels
Einstein and Planck explained how a photon is emitted
or absorbed by an atom
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Quantum Physics
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Energy levels, photons and spectral lines
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Quantum Physics
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Energy levels, photons and spectral lines
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Quantum Physics
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Energy levels, photons and spectral lines
Louis de Broglie showed that electrons are standing
waves that have mass and charge
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• They overlap the Bohr “orbits”
• Explains why electron energy levels are quantized and why
electrons do not spiral into the positive nucleus
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Quantum Physics
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Energy levels, photons and spectral lines
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Quantum Physics
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Elements
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Many substances but few “building blocks”
• Think of the number of words and letters in English
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The Periodic Table
• Tells us about the structure of elements and how they
behave
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Quantum Physics
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Elements
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Metals, nonmetals and metalloids
• Hydrogen is different than the others
Most elements are found in combination with other
elements
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