Nuclear Chemistry

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Nuclear Chemistry
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Element Stability

• Small mass atoms tend to be stable when the
  protonneutron ratio is 11
• Large mass atoms tend to be stable when the
  protonneutron ratio is 11.5

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Radioactivity is . . .

• The spontaneous decay of certain atoms to produce
  alpha, beta and gamma particles
• Radioactivity comes from the decay of the nucleus
  of an unstable atom

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Radioactive Decay Particles
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Nuclear Equations

• Mass number on each side of the arrow must have
  the same sum
• Atomic number on each side of the arrow must have
  the same sum
• Alpha decay of uranium-238 produces what isotope?

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Nuclear Equations

• Alpha
• Beta
• Gamma

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Nuclear Equations

• Electron capture

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Transmutation Reactions

• By bombarding elements with various particles
  (ranging from beta particles to elements) new
  elements can be created
• Nitrogen-14 bombarded with an alpha particle

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Transmutation Reactions

• Californium-250 bombarded with boron-11
• Phosphorus-31 bombarded with a neutron

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Half Life

• Defined as the amount of time required for one
  half of a radioactive substance to decay
• Half life is independent of the number of atoms
  started with

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Finding Half Life

• The equation for the number of atoms at any time
  is expressed as follows
• At the half life No/N 2, so

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Solve

• After 21 days a radioactive isotope has only one
  eighth of its original activity. What is the
  half-life of the radioactive isotope?

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Solve

• An isotope has a half-life of 3.00 min. What
  fraction of the original quantity remains after?
• 30.0 min
• 120.0 min

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Solve

• The half-life of 14C is 5585 years. A sample of
  carbon gave a count rate of 2.02. Another sample
  of carbon gave a count rate of 1.71. Calculate
  the age of the second sample.

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Solve

• In 6.00 hours, the activity of a radioactive
  compound falls from 999 counts per hour to 634
  counts per hour. What is the half-life of the
  isotope?

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Fission

• Process in which heavy nuclei absorb neutrons and
  split into roughly equal sized nuclei and more
  neutrons
• Can lead to a chain reaction if not contained

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Mass Deficit

• During nuclear reactions, the nuclei of the
  products is usually smaller than the nuclei of
  the reactants
• This lost mass is converted into energy
• Emc2

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Fusion

• Small nuclei can combine to form larger nuclei
• Very difficult to perform

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Some Uses of Radiation

• Medical
• 131I for thyroid and brain imaging
• 67Ga for lung function
• Isotopic dating
• Leak detection in pipes
• Fission in bombs and reactors