CHAPTER 22 Nuclear Chemistry

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CHAPTER 22Nuclear Chemistry
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Types of Radiation

• Isotopes - atoms of the same element with the
  same number of protons but different numbers of
  neutrons
• Radioisotopes isotope with an unstable nucleus
  that emits radiation to become a more stable
  nucleus
• Radioactive Decay spontaneous reaction in which
  unstable nuclei lose energy in the form of
  nuclear particles

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Nuclear Stability

• Why do atoms decay anyway
• need stable ratio of neutrons to protons
• Small atoms are stable with a 1 to 1 ratio of
  protons to neutrons
• As the atomic number increases, atoms tend to
  have more neutrons than protons with stable ratio
  increasing to 1 to 1.5
• The type of unbalance that is present in the
  nucleus determines the type of decay.

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Nuclear Stability
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Half-life

• Half-life (t½)
• Time required for half the atoms of a radioactive
  nuclide to decay.
• Shorter half-life less stable.

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Half-life
mf final mass mi initial mass n of half-lives
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Half-life

• Fluorine-21 has a half-life of 5.0 seconds. If
  you start with 25 g of fluorine-21, how many
  grams would remain after 60.0 s?

WORK mf mi (½)n mf (25 g)(0.5)12 mf 0.0061
g
GIVEN t½ 5.0 s mi 25 g mf ? total time
60.0 s n 60.0s 5.0s n 12
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Types of Nuclear Particles

• Alpha particle (a)
• Composition 2 protons, 2 neutrons
• Symbol 4He or a
• Charge 2
• Penetrating power low, stopped by paper or cloth

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• Beta particle (ß)
• Composition 1 electron
• Symbol -1 e
• Charge -1
• Penetrating power 100 times greater than alpha,
  stopped by wood or concrete

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• Gamma ray (? )
• Composition electromagnetic waves
• Symbol ?
• Charge 0
• Penetrating power 1000 times greater than beta,
  stopped by lead or 6 feet of concrete

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Types of Nuclear Decay

• Alpha Emission

Numbers must balance!!
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Types of Nuclear Decay

• Beta Emission

• Positron Emission

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Types of Nuclear Decay

• Electron Capture

• Transmutation
• One element becomes another.

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Fission vs. fusion
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F ission

• splitting a nucleus into two or more smaller
  nuclei
• 1 g of 235U 3 tons of coal

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F ission

• chain reaction - self-propagating reaction
• critical mass - mass required to sustain a
  chain reaction

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Fusion

• combining of two nuclei to form one nucleus of
  larger mass
• thermonuclear reaction requires temp of
  40,000,000 K to sustain
• 1 g of fusion fuel 20 tons of coal
• occurs naturally in stars

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Fission vs. Fusion
FISSION
FUSION

• fuel is abundant
• no danger of meltdown
• no toxic waste
• not yet sustainable

• 235U is limited
• danger of meltdown
• toxic waste
• thermal pollution