4'1 Refinements of the Atomic Model

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4.1 Refinements of the Atomic Model

• Mr. Chris Walters
• Williamstown Schools

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The Dual Nature of Light

• Experimentation has shown that light behaves as
  both a wave (energy) and as a particle (matter).
• This concept seems to defy logic but is supported.

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Electromagnetic Radiation

• A form of energy that displays wavelike behavior
  as it travels through space
• Travels at 3.0 x 108 m/sec in a vacuum (c)
• Has the measurable properties of wavelength (?)
  and frequency (?)
• The speed of light is equal to the product of
  wavelength times frequency.
• All the wavelengths of light form a continuous
  spectrum.
• One Hertz (Hz) is equal to 1 wave per second

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Visible Light

• that portion of the electromagnetic spectrum from
  wavelengths 375 nm to 725 nm
• Illustrated in 7 colors ROY G BIV (from longest
  wavelength to shortest)

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Light as Particles

• The wave theory of light encountered two problems
• It predicted that heated objects would give off
  ultraviolet light, they emit visible light
• It could not explain the Photoelectric effect

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Photoelectric Effect

• The Photoelectric effect is the emission of
  electrons by metals when light shines on them
• Only certain frequencies of light caused the
  effect

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Explanation - Planck

• Max Planck (1858-1947) proposed that energy was
  given off in specific quantities or Quanta.
  (singular Quantum)
• Planck proposed the following equation E h?,
  where h was a constant value.
• Plancks constant (h) 6.626 x 10 -34

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Continuation - Einstein

• An individual particle of light is called a
  photon.
• Einstein proposed that absorption of photons at
  certain quanta explained the photoelectric effect.

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Exciting Electrons to release light

• When atoms in the gaseous state are heated they
  increase in PE then return to original state as
  they emit light.
• As they are heated the electrons leave the ground
  state and become excited.
• They give off light in specific amounts (quanta).
• This can be illustrated in the line spectrum

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Bohr Model of the Atom

• Niels Bohr (1885-1962) proposed a model using
  this new information.
• It showed the orbits of the electrons a specific
  quantized distances from the nucleus.
• Bohrs model worked well on Hydrogen, but failed
  to match data with more complicated atoms and
  their line spectra.

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Spectroscopy

• A spectroscope is an instrument that separates
  light into a spectrum that can be analyzed.
• This allows the light to be examined and its
  atomic source discovered.

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Quantum Model

• Replaced the orbits of Bohr with regions of space
  in which the electrons are located called
  orbitals.
• Orbitals are quantized.
• Quantum theory mathematically explains the wave
  properties of electrons and other small
  particles.

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Louis deBroglie

• Louis deBroglie (1892-1987) proposed the dual
  nature of electrons.

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Schrodingers Wave Equation

• Erwin Schrödinger proposed his wave equation that
  mathematically explains electron action.
• These define the orbitals as regions where
  electrons are found with high probabilility.

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Heisenbergs Uncertainty Principle

• Werner Heisenberg contributed his Uncertainty
  Principle which states it is not possible to know
  both the velocity and position of a particle at
  the same time.

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Summary of Modern View

• Electrons are particles that can display
  wave-like properties.
• The electron cloud is a region around the nucleus
  where e- are likely to be found.
• The cloud is divided into regions called orbitals
  that are defined by Schrodingers wave equations.
  
• Each orbital has a distinct energy associated
  with it.
• It is not possible to know the location and the
  velocity of the electron at the same time.