Electron Theory

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Electron Theory

• How are the electrons arranged in an atom?

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I. Properties of Light as a Wave

• Electromagnetic radiation form of energy that
  exhibits wave-like behavior as it travels through
  space.
• Wavelength (m, cm, nm) distance between two
  peaks in a wave
• Frequency (Hz, 1/s) the number of waves that
  pass a given point in a specific time, usually
  one second

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Energy Relationships to Frequency and Wavelength

• All electromagnetic radiation moves at the speed
  of light
• 3.0 x 108 m/s or 186,000 mph
• High Energy (Ex gamma rays)
• Short wavelength High frequency
• Low Energy (Ex radio waves)
• Long wavelength Low frequency
• Which of these is more dangerous?

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II. Properties of Light as a Particle

• Quantum minimum quantity of energy that can be
  lost or gained by an atom
• Photon particle of electromagnetic radiation
  having zero mass and carrying a quantum of energy

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II. Properties of Light as a Particle

• The Dual-Wave Particle Nature of Light while
  light exhibits many wavelike properties, it can
  also be thought of as a stream of particles

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III. How Energy Affects Electrons in Atoms

• Bohr model of the atom the planetary model
  where the nucleus is orbited by electrons at
  different energy levels like planets around the
  sun
• Ground state lowest energy state of an atom
• Excited state state in which an atom has a
  higher potential energy that it has in its ground
  state

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III. How Energy Affects Electrons in Atoms

• Continuous spectrum the complete
  electromagnetic spectrum including all forms of
  energy (Ex rainbow)
• Line-emission spectrum when an atom is
  energized and the light given off is passed
  through a prism, a series of light with specific
  energy is emitted

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III. How Energy Affects Electrons in Atoms

• When an electron gains energy it moves to a
  higher energy level (shell).
• When an excited electron falls back down from its
  excited state to the ground state, it gives off a
  electromagnetic energy equal to the amount that
  it took to get it there. (Neon Lights)

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Locations of Electrons

• Level or Shell (n)
• Relative cloud size
• The maximum number of electrons possible in an
  energy level
• 2n2

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IV. Locations of Electrons

• Practice Problem
• Calculate the maximum number of e- possible in
  the following
• n2
• n3
• n7
• n9

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IV. Locations of Electrons

• Sublevel
• Cloud shape
• Represented by the following symbols
• s, p, d, f
• Sublevel Symbol Electrons
• Lowest s 2 e-
• Second p 6 e-
• Third d 10e-
• Fourth f 14e-

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IV. Locations of Electrons

• of sublevels is equal to value of the level
• Ex 1st level has 1 sublevel,
• 2nd level has 2 sublevels, etc
• Energy Level Sublevel e- in sublevels
  Total e-
• 1 s 2 2
• 2 s, p
  2 6 8
• 3 s, p, d 2
  6 10 18
• 4 s, p, d, f
  2 6 10 14 32

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V. Distribution of Electrons

• Aufbau Principle an electron occupies the
  lowest energy level that can receive it
• There is some overlapping of sublevels in atoms
  with higher atomic numbers.
• (Example the 4s sublevel fills before the 3d)
• Diagonal Rule gives a correct configuration for
  most atoms in the ground state
• 1s2
• 2s2 2p6
• 3s2 3p6 3d10
• 4s2 4p6 4d10 4f14
• 5s2 5p6 5d10 5f14
• 6s2 6p6 6d10 6f14
• 7s2 7p6 7d10 7f14
• 8s2 8p6 8d10 8f14

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V. Distribution of Electrons

• Examples
• Potassium (Z 19)
• Zirconium (Z 40)
• Yttrium (Z 39)
• Arsenic (Z 33)
• Tungsten (Z 74)