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Chapter 4 Nuclear Chemistry The Heart of Matter
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Radioisotopes

• Radioactive decay
• Many isotopes are unstable
• Nuclei that undergo radioactive decay
• May produce one or more types of radiation

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Natural Radioactivity

• Background radiation
• What occurs from natural sources
• Accounts for gt80 of radioactivity exposure

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Types of Radiation

• Ionizing radiation knocks electrons out of
• atoms or
  groups of atoms
• Produces charged species ions
• Charged species that cause damage

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Alpha Decay

• Nucleus loses ? particle
• Mass decreases by 4 and atomic number decreases
  by 2

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Beta Decay

• Nucleus loses ? particle
• No change in mass but atomic number increases

Positron Emission

• Loses a positron
• Equal mass but opposite charge of an electron
• Decrease in atomic number and no change in mass
• ?

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Electron Capture

• Nucleus absorbs an electron and then releases an
  X-ray
• Mass number stays the same and atomic number
  decreases

Gamma Radiation

• Release of high-energy photon
• ?
• Typically occurs after another radioactive decay
• No change in mass number or atomic number

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Nuclear Equations

• Elements may change in nuclear reactions
• Total mass and sum of atomic numbers must be the
  same
• MUST specify isotope

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Differences Between Chemical and Nuclear Reactions
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Example 4.1  Balancing Nuclear Equations
Write balanced nuclear equations for each of the
following processes. In each case, indicate what
new element is formed. a. Plutonium-239 emits an
alpha particle when it decays. b.
Protactinium-234 undergoes beta decay. c.
Carbon-11 emits a positron when it decays. d.
Carbon-11 undergoes electron capture.
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Half-Life

• Period for one-half of the original elements to
  undergo radioactive decay
• Characteristic for each isotope
• Fraction remaining
• n number of half-lives

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Example 4.2  Half-Lives
You obtain a new sample of cobalt-60, half-life
5.25 years, with a mass of 400 mg. How much
cobalt-60 remains after 15.75 years (three
half-lives)?
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Example 4.3  
You obtain a 20.0-mg sample of mercury-190,
half-life 20 min. How much of the mercury-190
sample remains after 2 hr?
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Radioisotopic Dating

• Use certain isotopes to estimate the age of
  various items
• 235U half-life 4.5 billion years
• Determine age of rock
• 3H half-life 12.3 years
• Used to date aged wines

Carbon-14 Dating

• 98.9 12C
• Produce 14C in upper atmosphere
• Half-life of 5730 years
• 50,000 y maximum age for dating

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Example 4.4  
A piece of fossilized wood has carbon-14 activity
one-eighth that of new wood. How old is the
artifact? The half-life of carbon-14 is 5730
years.
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Shroud of Turin

• Alleged burial shroud of Jesus Christ
• Contains faint human likeness
• First documented in Middle Ages
• Carbon-14 dating done in 1988
• Three separate labs
• Shroud 800 years old
• Unlikely to be burial shroud

Artificial Transmutation

• Transmutation changes one element into another
• Middle Ages change lead to gold
• In 1919 Rutherford established protons as
  fundamental particles
• Basic building blocks of nuclei

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Uses of Radioisotopes

• Tracers
• Easy to detect
• Different isotopes have similar chemical and
  physical properties
• Physical, chemical, or biological processes

• Agriculture
• Induce heritable genetic alterations mutations
• Preservative
• Destroys microorganisms with little change to
  taste or appearance of the food

Nuclear Medicine

• Used for two purposes
• Therapeutic treat or cure disease using
  radiation
• Diagnostic obtain information about patients
  health

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Radiation Therapy

• Radiation most lethal to dividing cells
• Makes some forms of cancer susceptible
• Try to destroy cancer cells before too much
  damage to healthy cells
• Direct radiation at cancer cells
• Gives rise to side effects

Diagnostic Uses

• Many different isotopes used
• See Table 4.6
• Can measure specific things
• Iodine-131 to locate tumors in thyroid
• Selenium-75 to look at pancreas
• Gadolinium-153 to determine bone mineralization

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Imaging

• Positron emission tomography (PET)
• Uses an isotope that emits a positron
• Observe amount of radiation released

Penetrating Power of Radiation

• The more mass the particle has, the less
  penetrating it is
• The faster the particle is, the more penetrating
  it is

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Prevent Radiation Damage

• To minimize damage
• Stay a distance from radioactive sources
• Use shielding need more with more penetrating
  forms of radiation

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Example 4.6
One of the isotopes used for PET scans is
oxygen-15, a positron emitter. What new element
is formed when oxygen-15 decays?
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Energy from Nucleus

• E mc2
• Lose mass, gain energy
• For chemical reactions, mass changes are not
  measurable
• For nuclear reactions, mass changes may be
  measurable

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Binding Energy

• Holds protons and neutrons together in the
  nucleus
• The higher the binding energy, the more stable
  the element

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Nuclear Fission

• Splitting the atom
• Break a large nucleus into smaller nuclei

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Nuclear Chain Reaction

• Neutrons from one fission event split further
  atoms
• Only certain isotopes, fissile isotopes, undergo
  nuclear chain reactions

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Manhattan Project

• How to sustain the nuclear reaction?
• How to enrich uranium to gt90 235U?
• Only 0.7 natural abundance
• How to make 239Pu (another fissile isotope)?
• How to make a nuclear fission bomb?

Radioactive Fallout

• Nuclear bomb detonated radioactive materials may
  rain down miles away and days later
• Some may be unreacted U or Pu
• Radioactive isotopes produced during the explosion

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Nuclear Power Plants

• Provide 20 U.S. electricity
• France gt70
• Slow controlled release of energy
• Need 2.53.5 235U
• Problem with disposal of radioactive waste

Nuclear Fusion

• Reaction takes smaller nuclei and builds larger
  ones
• Also called thermonuclear reactions

• Releases tremendous amounts of energy
• 1 g of H would release same as 20 tons of coal