Outline:41307

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Outline 4/13/07

• CAPA 19 due tonight
• Special seminar Friday 4pm
• Turn in Seminar reports to me

• Today Start Chapter 22

Nuclear Chemistry - Definitions - Nuclear
Stability - Modes of decay
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Nuclear Chemistry Some Definitions

• Nuclear chemistryabout nucleus
• Nucleus or nuclide ( a core made of protons and
  neutrons...called nucleons)
• Isotopes Nuclides of the same element (i.e.
  with same number of protons) but with a
  different mass (i.e. a different number of
  neutrons.)

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Remember Isotopes?

• Molar masses of elements weighted averages of
  all isotopes

Periodic Table
Amass number protons neutrons Zatomic
number protons Molar mass
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Example isotopic abundance

• Calculate the abundances of 63Cu and 65Cu if
  the atomic weight is 63.546 amu and the exact
  masses of the isotopes are 62.93 and 64.93 amu
  respectively.

(X)(62.93 amu) (1-X)(64.93 amu) 63.546 62.93X
64.93 - 64.93X 63.546 (62.93 - 64.93)X
63.546 - 64.93 -2X -1.384 X 0.692
1-X .308 69.2 63Cu 30.8 65Cu
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Nuclear Binding Energy

• If protons are positively charged, why does the
  nucleus stay together?

• Strong nuclear force a force stronger than the
  Coulombic repulsion of the protons in the nucleus
• The nucleus actually weighs less than the sum of
  its individual parts
• The difference in weight makes up the binding
  energy according to Emc2

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Binding energy

• Large amount of energy, small mass (Emc2
  )

• Holds the nucleons together strong
• Defines what makes a nucleus stable

Odd - Odd nuclei are unstable. N ? Z (light)
N ? 1.5 Z (heavy) Zmax (so far) ? 118
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Valley of stability
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So what happens to unstable nuclei?

• They decay Radioactivity

• One nucleus turns into another a process called
  transmutation

e.g. smoke detectors
Note that the reaction balances...
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Historical

• Types of radioactive decay
• Alpha (a), Beta (b), and Gamma (g)

• fission, fusion,
• positron (b), e- capture (EC).

• DEMO fiestaware, no-salt

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Nuclear Chemistry
Types of decays Examples a
b- g b EC fission fusion
alpha beta (electron) gamma beta
(positron) Electron Capture big ? 2 small
2 small ? big
smoke detectors
14C dating
Cancer therapy
PET scan
14C
Bombs
the sun
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Whence the electron in b-decay?
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Whence the electron in b-decay?
Not an atomic electron! (much more energetic)
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