Chapter 4 Arrangement of Electrons in Atoms

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Chapter 4Arrangement of Electrons in Atoms
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Section 4-1Development of a New Atomic Model
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What kept the negatively-charged electrons in the
space surrounding the positively charged nucleus
(Rutherford nuclear model)? ? ? ? ?
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This chapter will progress us in time to the

• Bohr model (1913)
• Quantum model (1926)

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Light can act as a WAVE.

• ? wavelength
• (lambda)
• ? frequency
• waves/sec
• (nu), measured in Hertz, Hz 1/s

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c ? ?

• c speed of light (3.00 x 108 m/s)
• (299,792,458 meters per second)
• What is the frequency of a beam of red light
  whose wavelength 659 nm?
• c ? ?
• 3.00 x 108 m/s (659 nm) ?

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What is the frequency of a beam of red light
whose wavelength 659 nm?

• c ? ?
• 3.00 x 108 m/s (659 nm) ?
• 3.00 x 108 m/s (659 x 10-9m) ?
• ? 4.55 x 1014 1/s 4.55 x 1014 Hz

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Is there a direct or inverse relationship between
wavelength and frequency?

• Inverse

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Visible light is the only electromagnetic (EM)
radiation we can see

• electromagnetic radiation (EM) form of energy
  that travels through space as a wave

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See page 92
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ROY G BIV
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Light can also act as a particle

• Supported by 2 experiments
• Photoelectric effect
• Hydrogen atom spectrum

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Photoelectric effect
Page 93
Why did light need a min frequency before it
would eject an electron from the metals
surface? Why did brighter light only release MORE
electrons of the same E..not more energetic
electrons??????
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Particle description of light

• Max Planck, 1900 studied emission of light by
  hot objects
• Proposed that energy is not emitted continuously
  but in small little packets called quanta This
  is a particle property
• quantum min amt of E than can be lost or
  gained by an atom
• Energy ? frequency

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Planck proposed the following relationship
between a quantum of energy and its frequency of
radiation

• Energy ? frequency
• E (some constant)( frequency )
• E h?
• where h Plancks constant 6.626 x 10-34 J s
  (or J/Hz)

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What is the energy of a beam of red light whose
wavelength 659 nm?

• From past notes, 659 nm light has a freq of
  4.55 x 1014 Hz (since c ?
  ?)
• E h?
• (6.626 x 10-34 J/Hz)( 4.55 x 1014Hz)
• 3.01 x 10-19 J

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Photoelectric effect is explained!
Metal must be struck by a photon possessing a
min. amt of E below this amt, the electron
wont leave the metal! More light of the same E
(same ?) just released more electronsnot more
energetic electrons.
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If light has a frequency of 6.26 x 1014 Hz, what
is its

• Wavelength ?
• Energy content ?
• Color ? (see chart in book)

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What do you know?

• ? 6.26 x 1014 Hz 6.26 x 1014 1/s
• ? ?
• Energy ?
• c ? ? and..
• E h ? where h6.626 x 10-34 J s or
• 6.626 x 10-34 J/Hz

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Hydrogens Line-Emission Spectrum
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• Absorption/emission lines for a given element are
  the fingerprints of the element

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• Ground state atoms whose electrons are in their
  lowest energy level
• Excited state an atom,having absorbed E, jumps
  its electron(s) to a higher E level. The electron
  must jump completely from one level to another.

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• De-excitation after a short time the electron
  falls back to a lower E level and emits a photon
  (packet of E) equivalent to the energy difference
  between the 2 steps. The photon will produce a
  spectral line with a discrete wavelength (color)
  associated with it.
• Continuous spectrumall wavelengths are present
  (i.e.sunlight)
• Emission (bright line) spectrum limited of
  specific bright lines that are produced by pass
  the light emitted by an excited atom through a
  prism

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• Absorption (dark line) spectrum light emitted by
  an excited atom passes through a substance that
  filters out certain wavelengths and thus produces
  a spectrum with missing (dark) lines.
• Bright lines of an emission spectrum are the SAME
  as the dark lines of an absorption spectrum for a
  given element.