Chapter 11 Modern Atomic Theory

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Chapter 11Modern Atomic Theory
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Electromagnetic Radiation

• Light is a form of electromagnetic (EM) radiation
• All forms of EM radiation are types of kinetic
  energy
• See page 306

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EM Radiation

• EM radiation can be described as traveling in
  waves or as packets of energy called photons

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EM Radiation

• Describe each form of EM radiation by its
• Wavelength
• Frequency
• Energy of its photon

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• All forms of EM radiation travel at the speed of
  light (c)
• Wavelength x frequency speed of light

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EM Radiation

• The longer the wavelength the
• lower the frequency and the lower the energy of
  the EM radiation
• The shorter the wavelength the
• higher the frequency and the higher the energy of
  the EM radiation

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EM Radiation

• Compare the wavelength frequency and energy of
• Ultraviolet light and infrared light

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EM Radiation

• The higher the energy of the EM radiation the
  more damaging it is to living tissue.
• CONSIDER GAMMA RAYS X-RAYS AND UV LIGHT

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Emission of Energy by Atoms

• Thanks to the work of Bohr we know that
• When atoms are energized by an input of energy
  their electrons are excited (energized)
• When excited electrons return to lower energy
  states they emits energy in the form of light.
• Emits photons of energy
• Energy of the photons emitted depends upon how
  excited the electron was.

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Bohr Experiment (1911)

• Bohr excited hydrogen atoms by running
  electricity through a tube of hydrogen gas.
• The gas gave off a pink light.

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Bohr Experiment (1911)

• Bohr aimed a beam of the pink light at a prism
• Found the pink light generated a line spectrum
  not a continuous spectrum
• Line spectrum specific colors of light observed
• Continuous spectrum all colors of light present

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Bohr Experiment (1911)

• He observed 4 bands of color (pg 310)
• Purple (410 nm)
• Blue (434 nm)
• Green (486 nm)
• Red (656 nm)

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Bohr Experiment (1911)

• He then calculated the energy of each color of
  light
• _____________ was the highest energy and
  _____________ was the lowest energy.

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Bohrs Interpretation of the Data

• The electrons circle the nucleus in orbits of
  specific energies.
• Larger orbits are of higher energy than smaller
  orbits

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Bohrs Interpretation of the Data

• Electrons are always in one of the circular
  orbits.
• The electricity excites electrons and allows them
  to move to higher energy orbits.

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Bohrs Interpretation of the Data

• When the excited electrons return to lower energy
  orbits they emit energy in the form of light.
• The difference in energy levels between the
  orbits determines the energy of the light given
  off.

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Bohrs Interpretation of the Data

• Because only certain wavelengths of light are
  emitted only certain energy changes are occurring
• 4 bands of light therefore 4 possible energy
  changes are possible
• Say energy levels are quantized meaning only
  specific energy levels are available to electrons.

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Bohrs Model

• When Bohrs mathematical approach was applied to
  other elements it didnt work.
• Bohrs model of the atom has been revised to
  replace the circular orbits with wave mechanical
  model of the atom

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Modern Atomic Structure

• Still picture electrons to be at specific energy
  levels but no longer picture them as traveling
  in circular orbits.
• The current model of the atom locates electrons
  in orbitals.

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Modern Atomic Structure

• Orbitals are very different than Bohrs orbits
• Read the firefly analogy on page 313

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Orbitals

• Each orbital is of a specific energy size and
  shape
• Each orbital can hold a maximum of 2 electrons of
  opposite spin (Pauli exclusion principle)

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Orbitals

• The exact path of an electron in an orbital is
  not known.
• Heisenberg uncertainty principle states that it
  is impossible to determine the location and path
  of an electron at the same time

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Orbitals

• Orbital shapes describe the region in space where
  an electron will be found 90 of the time.

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Modern Atomic Theory

• Atoms have specific energy levels in which
  electrons may be found.
• Called Principal Energy Levels (PEL)
• PEL farther from the nucleus are larger and of
  higher energy.
• Assign a number (n) to each PEL
• See board

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Modern Atomic Theory

• Within each PEL are sublevels
• Sublevels are named s p d and f
• The larger the PEL the more sublevels it contains

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Modern Atomic Theory
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Modern Atomic Theory
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Modern Atomic Theory

• Sublevels contain orbitals.

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Describing Orbitals

• See pages 314/315 for diagrams of the orbitals
• S orbitals are spherical
• The 3 p orbitals are
• shaped

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Putting it All Together

• Unless they are excited electrons always occupy
  the lowest energy orbital with room.
• Electrons enter orbitals of a given sublevel one
  at a time before pairing up (Hunds rule)
• Consider 2 electrons in a p sublevel

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The fun part!

• Our goal is to write the following for atoms and
  ions
• Electron configuration
• Box/energy diagram
• Lewis dot symbol
• Our goal is also to
• Identify core and valence electrons

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Terms

• Electron configuration shows the number of
  electrons in each sublevel
• Box/energy diagram shows the number of
  electrons in each orbital
• Orbitals are shown as boxes
• electrons are shown as arrows

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Terms

• Lewis Dot Symbol shows the valence electrons as
  dots around the symbol for the element
• Maximum of 2 electrons per side of the symbol

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Terms

• Valence electrons all the electrons in the
  highest occupied PEL
• Valence electrons are the ones involved in
  bonding
• Core electrons all electrons not considered
  valence electrons

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You will be given this.

• Sublevels listed from lowest energy to higher
  energy
• 1s 2s 2p 3s 3p 4s 3d 4p 5s 4d 5p.