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Nuclear Chemistry powerpoint

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									NUCLEAR CHEMISTRY
Chapter 25
Introduction to Nuclear Chemistry
   Nuclear chemistry is the study of the structure of
                                and the
    they undergo.
Chemical vs. Nuclear Reactions
Chemical Reactions   Nuclear Reactions

Occur when bonds     Occur when nuclei
are broken           emit particles and/or
                     rays
Chemical vs. Nuclear Reactions
Chemical Reactions            Nuclear Reactions
Occur when bonds are broken   Occur when nuclei emit particles and/or
                              rays

Atoms remain        Atoms often
unchanged, although converted into atoms
they may be         of another element
rearranged
Chemical vs. Nuclear Reactions
Chemical Reactions                      Nuclear Reactions
Occur when bonds are broken             Occur when nuclei emit particles and/or
                                        rays
Atoms remain unchanged, although they   Atoms often converted into atoms of
may be rearranged                       another element

Involve only valence May involve protons,
electrons            neutrons, and
                     electrons
Chemical vs. Nuclear Reactions
Chemical Reactions                      Nuclear Reactions
Occur when bonds are broken             Occur when nuclei emit particles and/or
                                        rays
Atoms remain unchanged, although they   Atoms often converted into atoms of
may be rearranged                       another element
Involve only valence electrons          May involve protons, neutrons, and
                                        electrons

Associated with small Associated with
energy changes        large energy
                      changes
Chemical vs. Nuclear Reactions
Chemical Reactions                      Nuclear Reactions
Occur when bonds are broken             Occur when nuclei emit particles and/or
                                        rays
Atoms remain unchanged, although they   Atoms often converted into atoms of
may be rearranged                       another element
Involve only valence electrons          May involve protons, neutrons, and
                                        electrons
Associated with small energy changes    Associated with large energy changes

Reaction rate                           Reaction rate is not
influenced by                           influenced by
temperature, particle                   temperature, particle
size, concentration, etc.               size, concentration, etc.
The Discovery of Radioactivity (1895 –
1898):
                      found that invisible rays were
    emitted when electrons bombarded the surface of
    certain materials.
   Becquerel accidently discovered that
    phosphorescent                   salts produced
    spontaneous emissions that darkened photographic
    plates
The Discovery of Radioactivity (1895 –
1898):


   isolated the components (                 atoms)
    emitting the rays
                               – process by which
    particles give off
                        – the penetrating rays and
    particles                by a radioactive source
The Discovery of Radioactivity (1895 –
1898):
   identified 2 new elements,                       and
                   on the basis of their radioactivity
   These findings                           Dalton’s
    theory of indivisible atoms.
The Discovery of Radioactivity (1895 –
1898):
                     – atoms of the              element
    with different numbers of
                                – isotopes of atoms with
                     nuclei (too           /
    neutrons)
                                          – when unstable
    nuclei         energy by emitting
    to attain more                     atomic
    configurations (                           process)
Alpha radiation
   Composition – Alpha particles, same as helium nuclei
                              4
   Symbol – Helium nuclei, 2He, α
   Charge – 2+
   Mass (amu) – 4
   Approximate energy – 5 MeV
   Penetrating power – low (0.05 mm body tissue)
   Shielding – paper, clothing
Beta radiation
   Composition – Beta particles, same as an electron
   Symbol – e-, β
   Charge – 1-
   Mass (amu) – 1/1837 (practically 0)
   Approximate energy – 0.05 – 1 MeV
   Penetrating power – moderate (4 mm body tissue)
   Shielding – metal foil
Gamma radiation
   Composition – High-energy electromagnetic
    radiation
   Symbol – γ
   Charge – 0
   Mass (amu) – 0
   Approximate energy – 1 MeV
   Penetrating power – high (penetrates body easily)
   Shielding – lead, concrete
Review of Atomic Structure
Nucleus            Electrons

99.9% of the mass 0.01% of the mass
1/10,000 the size of
the atom
Review of Atomic Structure
Nucleus                         Electrons
99.9% of the mass               0.01% of the mass
1/10,000 the size of the atom

Composed of                     Composed of
protons (p+) and                electrons (e-)
neutrons (n0)
Review of Atomic Structure
Nucleus                                 Electrons
99.9% of the mass                       0.01% of the mass
1/10,000 the size of the atom
Composed of protons (p+) and neutrons   Composed of electrons (e-)
(n0)

Positively charged                      Negatively charged
Review of Atomic Structure
Nucleus                                 Electrons
99.9% of the mass                       0.01% of the mass
1/10,000 the size of the atom
Composed of protons (p+) and neutrons   Composed of electrons (e-)
(n0)
Positively charged                      Negatively charged

Strong nuclear force Weak electrostatic
(holds the nucleus   force (because they
together)            are charged
                     negatively
Chemical Symbols
   A chemical symbol looks like…


                      14
                       6   C


   To find the number of           , subtract the
                    from the
Nuclear Stability
   Isotope is completely stable if the nucleus will
    spontaneously                         .
   Elements with atomic #s       to      are
                            .
           ratio of protons:neutrons (          )
   Example: Carbon – 12 has         protons and
    neutrons
Nuclear Stability
   Elements with atomic #s      to      are
                                      .
            ratio of protons:neutrons (p+ : n0)
   Example: Mercury – 200 has           protons and
    neutrons
Nuclear Stability
 Elements with atomic #s         are
 and                      .
 Examples:                 and
Alpha Decay
   Alpha decay – emission of an alpha particle ( ),
    denoted by the symbol 42
                                    , because an α has 2
    protons and 2 neutrons, just like the He nucleus.
    Charge is     because of the 2                    .
   Alpha decay causes the               number to
    decrease by      and the               number to
    decrease by .
                                   determines the
    element. All nuclear equations are                  .
   Alpha Decay
    Example 1: Write the nuclear equation for the
     radioactive decay of polonium – 210 by alpha
     emission.
 Step 1: Write the element that you are starting with .
 Step 2: Draw the arrow.
Mass #



Atomic # Step 3: Write the alpha particle.
Step 4: Determine the other product (ensuring everything is
balanced).
  Alpha Decay
     Example 2: Write the nuclear equation for the
      radioactive decay of radium – 226 by alpha
      emission.


Mass #



Atomic #
Beta decay
   Beta decay – emission of a beta particle ( ), a fast
    moving                   , denoted by the symbol
        0
    or -1        . β has insignificant mass ( ) and the
    charge is   because it’s an                 .

   Beta decay causes      change in          number
    and causes the             number to increase by .
  Beta Decay
     Example 1: Write the nuclear equation for the
      radioactive decay of carbon – 14 by beta emission.



Mass #



Atomic #
  Beta Decay
     Example 2: Write the nuclear equation for the
      radioactive decay of zirconium – 97 by beta
      decay.


Mass #



Atomic #
Gamma decay
   Gamma rays – high-energy
    radiation, denoted by the symbol      .
   γ has no mass ( ) and no charge ( ). Thus, it
    causes        change in         or
    numbers. Gamma rays almost
    accompany alpha and beta radiation. However,
    since there is      effect on mass number or atomic
    number, they are usually                from nuclear
    equations.
Transmutation
                                 –
    the                        of one atom of one
    element to an atom of a different element
    (                        decay is one way that this
    occurs!)
Review
  Type of     Particle        Change in Change in
Radioactive   Emitted          Mass #   Atomic #
   Decay
                       4
   Alpha       α       2 He      -4        -2
    Beta       β        0
                       -1e        0        +1
 Gamma             γ              0         0
Half-Life
                    is the          required for
    of a radioisotope’s nuclei to decay into its products.
   For any radioisotope,
          # of ½ lives           % Remaining
               0                     100%
               1                      50%
               2                      25%
               3                     12.5%
               4                     6.25%
               5                    3.125%
               6                   1.5625%
Half-Life
Half-Life
   For example, suppose you have 10.0 grams of
    strontium – 90, which has a half life of 29 years.
    How much will be remaining after x number of
    years?                 # of ½ lives Time (Years) Amount
                                                     Remaining (g)
   You can use a table:
                             0            0            10
                             1            29           5
                             2            58           2.5
                             3            87           1.25
                             4            116          0.625
Half-Life
   Or an equation!
Half-Life
   Example 1: If gallium – 68 has a half-life of 68.3
    minutes, how much of a 160.0 mg sample is left
    after 1 half life? ________
    2 half lives? __________ 3 half lives? __________
Half-Life
   Example 2: Cobalt – 60, with a half-life of 5 years,
    is used in cancer radiation treatments. If a hospital
    purchases a supply of 30.0 g, how much would be
    left after 15 years? ______________
Half-Life
   Example 3: Iron-59 is used in medicine to diagnose
    blood circulation disorders. The half-life of iron-59
    is 44.5 days. How much of a 2.000 mg sample will
    remain after 133.5 days? ______________
Half-Life
   Example 4: The half-life of polonium-218 is 3.0
    minutes. If you start with 20.0 g, how long will it
    take before only 1.25 g remains? ______________
Half-Life
   Example 5: A sample initially contains 150.0 mg of
    radon-222. After 11.4 days, the sample contains
    18.75 mg of radon-222. Calculate the half-life.
Nuclear Reactions
   Characteristics:
   Isotopes of one element are                  into
    isotopes of another element
   Contents of the               change
                amounts of                are released
Types of Nuclear Reactions

                         decay – alpha and beta
    particles and gamma ray emission
   Nuclear                          - emission of a
               or
Nuclear Fission
                    -                  of a nucleus
   - Very heavy nucleus is split into
    approximately                 fragments
   -               reaction releases several neutrons
    which             more nuclei
   - If controlled, energy is released
    (like in                                 ) Reaction
    control depends on reducing the                  of the
    neutrons (increases the reaction rate) and
                         extra neutrons (     creases the
    reaction rate).
Nuclear Fission
   - 1st controlled nuclear reaction in December 1942.
    1st uncontrolled nuclear explosion occurred July
    1945.
   - Examples – atomic bomb, current nuclear power
    plants
Nuclear Fusion
                    -                      of a nuclei
   - Two           nuclei combine to form a
    heavier nucleus
   - Does not occur under standard conditions (   repels )
   - Advantages compared to fission -                     ,

   - Disadvantages - requires               amount of
    energy to            , difficult to
   - Examples – energy output of stars, hydrogen bomb,
    future nuclear power plants

								
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