Arrangement of Electrons in Atoms Part One

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Arrangement of Electronsin AtomsPart One

• Learning Objectives
• Read Pages 97-106
• Asgn 16 103/1-6

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Section 1 Light and Electrons

• Explain the mathematical relationship amount the
  speed, wavelength, and frequency of
  electromagnetic radiation.
• Discuss the dual wave-particle nature of light.
• Discuss the significance of the photoelecvtric
  effect and the line-emission spectrum of H to the
  development of the atomic model.
• Describe the Bohr model of the H atom.

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Section 2 Quantum Model

• Discuss De Broglies role in the development of
  the quantum model of the atom.
• Compare and contrast the Bohr model and the
  quantum model of the atom.
• Explain how the Heisenberg uncertainty principle
  and the Schrodinger wave equation led to the idea
  of atomic orbitals.

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• Electromagnetic Radiation (EMR) or light is a
  form of energy that moves as a wave through
  space.
• Electromagnetic Spectrum is made up of many kinds
  of EMR visible, X rays, ultraviolet, infrared,
  microwaves, and radiowaves.

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Electromagnetic (E-M) Waves (LIGHT!) Do not
require a medium through which to travel Light
travels at 3.0 x 108 m/s in a vacuum or air Its
wavelength and frequency varies according to the
type of E-M wave
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Higher frequency ? Greater energy ? More
penetration

• What type has
• Greatest frequency?
• Less frequency than infrared light?

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c ln

• c , the speed of light which is 3x108 m/s in a
  vacuum or air. Units m/s
• l, wavelength or distance between corresponding
  points on adjacent waves
• Units m or nm
• n, frequency or number of waves passing a point
  in a given amount of time. Units Hertz, Hz or
  1/s or s-1

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Light Problems What is the frequency of light
whose wavelength is 600 nm?

• nm means 10-9 m
• c ln --gt n c/l
• 3x108 m 5 x 1014 s-1
• 600x10-9 m s

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Photoelectric Effect

• This is the emission of electrons from a metal
  when electromagnetic radiation shines on the
  metal.

P. E. shows that energy is emitted in small,
specific packets called quanta. A quantum of
energy is the minimum quantity of energy that can
be lost or gained by an atom.
The photoelectric effect showed that light
behaves as particles, too!
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E h n

• E, energy of a quantum of radiation in joules, J
• h, Plancks constant is 6.626 x 10-34 Js
• n, frequency in s-1
• Problem What is the frequency of a photon whose
  energy is 3.4 x 10-19 J?
• n E/h 3.4 x 10-19 J / 6.626 x 10 -34 Js
• n 5.1 x 1014 s-1
• Wavelength-frequency relationship was
  proposed by Planck in 1900.

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• Einstein explained the photoelectric effect was
  due to metal absorbing energy in discrete amounts
  of photons.
• Ground state lowest energy state of an atom
• Excited state state where an atom has a higher
  potential energy than ground state.

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webexhibits.org
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Tutorvista.com
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Bohr Model

• 1913 Niels Bohr proposed a hydrogen atom model
  where electrons circle the nucleus only in
  allowed paths or orbits with a definite amount of
  energy.
• If an electron absorbs energy, it can go to a
  higher level.
• If in a higher energy level, an electron can
  emit a certain amount of energy to move to a
  lower level.

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• 
  chemweb.ucc.ie

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Quantum Model of the Atom

• Questions were unanswered regarding how electrons
  could be particles yet they gave off waves of
  light.
• De Broglie suggested that electrons could be
  considered waves confined to space around a
  nucleus only at specific frequencies.
• Diffraction experiments proved that electron
  beams can interfere with each other and produce
  areas of low energy and high energy areas as a
  result of interference.

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• Heisenberg Uncertainty Principle (1927) it is
  impossible to determine simultaneously both the
  position and velocity of an electron or any other
  particle.
• Schrodinger Wave Equation (1926) - developed an
  equation that treated electrons in atoms as
  waves.
• Heisenberg and Schrodinger laid the foundation
  for mathematical descriptions of wave properties
  of very small particles such as electrons the
  probable location of electrons around the
  nucleus.
• AKA Quantum Theory and Quantum Numbers.

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• End of Section 1 and part of Section 2 of Chapter
  4
• Arrangement of Electrons in Atoms

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