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Nuclear Chemistry

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Title: Nuclear Chemistry


1
Nuclear Chemistry
  • Chapter 23
  • 23.1-23.6

2
Nuclear Chemistry
  • Nuclear Chemistry- the study of reactions
    involving changes in atomic nuclei.
  • Importance
  • Disadvantages

3
Nuclear Reactions
  • Except for Hydrogen, all nuclei contain particles
    called protons and neutrons.
  • Nuclei can be stable or unstable.
  • Unstable Nuclei emit particles and/or
    electromagnetic radiation spontaneously.
  • Phenomenon is called Radioactivity.
  • Nuclear Transmutation- results from the
    bombardment of nuclei by neutrons, protons or
    other nuclei.

4
Nuclear Reactions
  • Atomic number (Z) number of protons in nucleus
  • Mass number (A) number of protons number of
    neutrons
  • atomic number (Z) number
    of neutrons

5
Nuclear Reactions
6
Balancing Nuclear Equations
  • Conserve mass number (A).

The sum of protons plus neutrons in the products
must equal the sum of protons plus neutrons in
the reactants.
235 1 138 96 2x1
7
Balancing Nuclear Equations
  • Conserve atomic number (Z) or nuclear charge.

The sum of nuclear charges in the products must
equal the sum of nuclear charges in the reactants.
92 0 55 37 2x0
8
Balancing Nuclear Equations
212Po decays by alpha emission. Write the
balanced nuclear equation for the decay of 212Po.
212 4 A
A 208
Z 82
84 2 Z
23.1
9
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10
Chemical Reactions vs. Nuclear Reactions
11
Nuclear Stability
  • Nucleus is very small
  • Contributes most of weight of atom
  • Extremely high density
  • Even higher of particles

12
Nuclear Stability
  • Particles repel/attract each other
  • neutron-to-proton ratio
  • Predicting stability
  • Magic numbers 2,8,20,50,82,126
  • Even numbers of neutrons and protons vs. odd
    numbers
  • All isotopes of elements with atomic numbers
    higher than 83 are radioactive.
  • All isotopes of Tc and Pm are radioactive.

13
n/p too large
beta decay
n/p too small
positron decay or electron capture
14
Nuclear Stability
Beta decay
Decrease of neutrons by 1
Increase of protons by 1
23.2
15
Nuclear Stability
Positron decay
Increase of neutrons by 1
Decrease of protons by 1
16
Nuclear Stability
Electron capture decay
Increase of neutrons by 1
Decrease of protons by 1
17
Nuclear Stability
Alpha decay
Decrease of neutrons by 2
Decrease of protons by 2
18
Nuclear Binding Energy
  • Nuclear Binding Energy- the energy required to
    break up a nucleus into its component protons and
    neutrons.
  • Necessity?
  • Mass Defect
  • Einsteins Theory of Relativity

E mc2
19
Nuclear Binding Energy
E mc2
BE 9 x (p mass) 10 x (n mass) 19F mass
BE (amu) (9 x 1.007825) (10 x 1.008665)
18.9984
BE 0.1587 amu
1 amu 1.49 x 10-10 J
BE 2.37 x 10-11J
20
Nuclear Binding Energy
1.25 x 10-12 J
21
Nuclear Binding Energy
22
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23
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24
Natural Radioactivity
  • Outside the belt of stability, nuclei are
    radioactive.
  • Radioactive nuclei spontaneously emit radiation.
  • a particles, ß particles, ? rays, etc.
  • Disintegration of radioactive nucleus leads
  • to a decay series.

25
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26
Radioactive Decay--Dating
  • Uranium decay
  • After time, half of parent exsists
  • Equal amounts of parent and daughter
  • Age?

27
Nuclear Transmutations
  • Rutherford, 1919
  • Artificial Radioactivity
  • Nitrogen bombarded by a particles

28
Nuclear Transmutation
  • Notation for reactions
  • First Isotope (bombarding particle, ejected
    particle) Final Isotope
  • Notation for Nitrogen-14 bombarded with a
    particle.

29
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30
Transuranium Elements
  • Synthetic elements
  • Atomic Numbers greater than 92
  • Particle Accelerator necessary for preparation

31
Particle Accelerator
32
Nuclear Fission
  • Nuclear Fission- the process in which a heavy
    nucleus (mass number gt 200) divides to form
    smaller nuclei of intermediate mass and one or
    more neutrons.
  • Energy is released.
  • Uranium-235 was the first element discovered to
    go through nuclear fission.

33
Nuclear Fission
34
Nuclear Fission
  • Nuclear chain reaction is a self-sustaining
    sequence of nuclear fission reactions.

The minimum mass of fissionable material required
to generate a self-sustaining nuclear chain
reaction is the critical mass.
35
Chain Reaction
36
The Atomic Bomb
37
Nuclear Reactors
  • Peaceful application of nuclear fission
  • Generates electricity from chain reactions
  • Provides 20 of electricity in U.S.
  • Light water reactors Heavy water reactors
    Breeder reactors

38
Light Water Reactors
  • Most U.S. nuclear reactors are light water
  • Light Hydrogen
  • Use Uranium-235 under controlled conditions
  • Releases large quantities of steam
  • Steam drives electric generators
  • Needs large amounts of coolant
  • Plants built by lakes and rivers
  • Large amounts of thermal pollutant

39
Light Water Reactors
40
Heavy Water Reactors
  • Uses Deuterium D2O
  • D absorbs neutrons less efficiently than H
  • Does not require U-235
  • Neutrons leak out of reactor
  • Expensive to prepare D2O
  • Environmentally friendly

41
Breeder Reactors
  • Breeder Reactor- uses uranium fuel, but unlike a
    conventional nuclear reactor, it produces more
    fissionable materials than it uses.
  • Converts uranium-238 to plutonium-239 in a 3 step
    process.
  • Plutonium-239 undergoes fission
  • Reactor produces 1 mole of p-239 for every 1 mole
    used.
  • Takes 7-10 years for complete regeneration.

42
Hazards of Nuclear Energy
  • Production of radioactive isotopes with long
    half-lives (24,400 years)
  • Radioactive and toxic substances
  • Three-mile Island Reactor- radiation escaped
  • Chernobyl Nuclear Plant- fire and explosion
  • Accidents
  • Waste Disposal

43
Nuclear Fusion
  • Nuclear Fusion- the combining of small nuclei
    into larger ones.
  • Two small nuclei can combine and release large
    amounts of energy
  • To occur, the nuclei must be in an environment
    with high temperature.
  • Thermonuclear Reactions
  • Nuclear fusion occurs constantly on the Sun.

44
Nuclear Fusion
  • How do we get it to occur?
  • Container?

45
The Hydrogen Bomb
  • Thermonuclear Bomb
  • All power and no control
  • Fusion reaction then fission reaction
  • Fusion reaction creates high temp. for fission
    reaction
  • Bombs usually contain Co-59 and upon explosion
    convert to Co-60
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