Nuclear%20Chemistry

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Nuclear Chemistry
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Isotopes-Review

• Isotopes are atoms of the same element that have
  the same of protons but different of neutrons
  or mass.
• X

Atomic mass
Atomic number
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• When the size and mass of the nucleus becomes
  large (greater than atomic 83), the element is
  known to be radioactive (unstable) because it
  decays.
• Examples
• Pu-239 (94 protons), U-238 (92 protons)
• When the ratio of neutrons to protons is greater
  than 11 (for light nuclei) , the element is also
  radioactive.
• Examples
• Carbon-14, Lithium-7

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Natural radioactivity

• Occurs when nuclei are unstable.
• For any element, an isotope that is unstable is
  called a radioisotope.

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Particles Emitted

• When a nucleus decays, it emits particles.

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Alpha Decay

• when an unstable nucleus emits an alpha
  particle, this is called alpha decay.

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Beta Decay

• When an unstable nucleus emits a beta particle,
  this is called a beta decay.

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Positron Emission

• When an unstable nucleus emits a positron, it is
  called positron emission

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Writing Nuclear Equations

• Obeys laws of conservation of mass and charge.

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Natural Transmutation

• Begins with one nucleus that spontaneously
  decays.
• Always has ONE REACTANT.

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Artificial Transmutation

• Bombardment of the nucleus with high energy
  particles.
• Always has TWO REACTANTS.

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Fission Reactions

• Involve the splitting of a heavy nucleus to
  produce lighter nuclei.

Fission reactions produce/capture neutrons. They
can become involved in another fission reaction.
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• If the number of neutrons released is not
  controlled a chain reaction will occur.
• This is the type of reaction used in nuclear
  bombs.

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Fusion Reactions

• Involves the combining of nuclei to produce
  heavier ones.

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• In fission and fusion reactions, there appears to
  be a loss of mass. However, this mass has been
  converted to energy by the equation
• E mc2

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Nuclear vs. Chemical Fission vs. Fusion

• The energy of nuclear reactions is much greater
  than the energy associated with chemical
  reactions.
• The energy of fission is greater than the energy
  of fusion.

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Half-Life

• Radioactive substances decay at a rate that is
  not dependent on temperature, pressure, or
  concentration.
• Half-life is the time it takes for half the atoms
  in a given sample of an element to decay.
• See Table N for half-lives and modes.

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Uses of Radioactivity

• Dating? C-14 used to date organic remains
  U-238Pb-206 for minerals

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Uses continued

• Chemical tracers? can follow the path of a
  material (ex fertilizer)
• Industrial applications? can test thickness or
  strength of materials

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Uses continued

• Medical applications? must have short half-life
  and quickly eliminated from body, I-131 thyroid,
  Tc-99/Co-60 cancer

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Dangers of Radioactivity

• Damage to tissue
• Gene mutation