The Development of a New Atomic Model

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The Development of a New Atomic Model

• Rutherford- did not explain how the atoms
  negatively charged particles are distributed in
  the space surrounding its positively charged
  nucleus.

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The New Atomic Model

• Researcher used investigations into the
  absorption and emission of light
• Studies revealed a relationship beteen light an
  atoms electrons
• New understanding about the nature of energy,
  matter, and atomic structure.

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Properties of Light

• Before 1900, light was thought to behave solely
  as a wave
• Wavelike description
• It is type of electromagnetic radiation
• Forms part of the electromagnetic spectrum
• Significant wavelike motion characterized by
  wavelength and frequency
• Wavelength (?) is the distance between
  corresponding points on adjacent waves.
• Frequency (v) is the number of waves that pass a
  specific point in a given time, usually one
  minute.

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Frequency and wavelength are mathematically
related to each other

• c?v c is the speed of light, a constant
• There for ?, wavelength in m, is inversely
  proportional to v, frequency in s-1.
• As wavelength decreases frequency increases and
  vice versa

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The Photoelectric Effect

• The photoelectric effect refers to the emission
  of electron when light is shines on a metal.

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The Photoelectric Effect

• The mystery was..
• No electron would be emmited if the lights
  frequency (v) was below a certain minimum.
• No matter how intense (W) the light was.
• Wave theory state that light of any frequency
  could supply enough energy to eject an electron.

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The Particle Description of Light

• Max Planck (1900 German Physicist)
• Studied emission of light by hot objects
• He proposed the hot objects do not emit
  electromagnetic energy continuously (as would be
  expected if all we were dealing with was a wave)

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The Particle Description of Light

• Quantum- a measure of energy that is the minimum
  quantity of energy that can be lost or gain by an
  atom
• Planck proposed a relationship between a quantum
  of energy and the frequency of radiation
• Ehv
• E energy in joules, v is frequency (s-1),
• h a fundamental physical constant now know as
  Plancks constant 6.626x 10 -34

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The Duality of particles and waves

• Albert Einstein expanded on Plancks work and
  proposed a radical idea
• Electromagnetic radiation has a dual
  wave-particle nature
• While like light act like a wave
• It is a stream of particles
• Each particle carries a quantum of energy
• These particles are called photons
• These particles have zero mass but carry a
  quantum of energy

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This explained the photoelectric effect

• Einstein explained
• Electromagnetic radiation is only absorbed by
  matter in whole numbers
• In order for an electron to be rejected from the
  surface of the metal it must be struck by a
  single photon possessing at least a minimum
  energy required to knock the electron off.
• Every metal has a different frequency

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Home work

• Pages 124-125
• 1-25
• Complete sentences
• If it is a multiple choice problem, select the
  letter choice them write a true complete sence
  out of the question and the choice DO NOT COPY
  THE QUESTIONS
• If it is a calculation, show equation used and
  ALL work
• Have a great Thanksgiving!!!