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Chapter 20
Nuclear Chemistry
20.1 Nuclei and Nuclear Reactions
• Radioactive decay – emission of
particles and/or electromagnetic radiation
by unstable nuclei
• Radioactivity - Spontaneous emission of
particles or electromagnetic radiation
• Nuclear transmutation, results from the
bombardment of nuclei by neutrons,
protons, or other nuclei.
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Radioactive decay and nuclear transmutation are
nuclear reactions, which differ significantly from
ordinary chemical reactions.
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• The symbols for subatomic particles are
as follows:
• In balancing any nuclear equation, we
must balance the total of all atomic
numbers and the total of all mass numbers
for the products and reactants.
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Identify X in the following nuclear equation.
78
33
As  X 

0
1
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78
33
As X 
A
Z

0
1
S reactant mass numbers = S product mass numbers
78  A  0
78  A
S reactant atomic numbers = S product atomic numbers
33  Z  ( 1)
34  Z
Therefore, X is Se or
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34
Se
6
20.2 Nuclear Stability
• Nuclear stability determined by a balance
between
– Coulombic repulsions
– Short range nuclear attractions (very strong)
– If replusions > attractions, the nucleus is
unstable
– If attractions > replusions, the nucleus is
stable
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• Patterns of nuclear stability
– Nuclei containing a magic number of protons
and/or neutrons are stable.
• The numbers 2, 8, 20, 50, 82, and 126 are
called magic numbers.
– There are many more stable nuclei with even
numbers of both protons and neutrons than
with odd numbers of these particles.
– All isotopes of the elements with atomic
numbers higher than 83 are radioactive.
– All isotopes of technetium (Tc, Z = 43) and
promethium (Pm, Z = 61) are radioactive.
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Above the belt
Below the belt
 particle emission
positron emission
electron capture
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• Nuclear Binding Energy
– Quantitative measure of nuclear stability
– The energy required to break up a nucleus
into its component protons and neutrons.
– Represents the conversion of mass to energy
that occurs during an exothermic nuclear
reaction.
– The difference between the mass of an atom
and the sum of the masses of its protons,
neutrons and electrons is called the mass
defect.
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– According to Einstein’s mass-energy
equivalence relationship (E = mc2, where E
is energy, m is mass, and c is the velocity of
light), the energy released is
DE  (Dm)c
2
– where DE and Dm are defined as follows:
DE  energy of products - energy of reactants
Dm  mass of products - mass of reactants
DE  nuclear binding energy
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nuclear binding energy
nuclear binding energy per nucleon 
number of nucleons
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Calculate a) the nuclear binding energy in
kilojoules/mol and b) the nuclear binding energy
208
in joules per nucleon of 83 Bi . The exact atomic
mass of bismuth is 208.9804.
mass n  1.008665
1
0
mass H  1.007825
1
1
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a) Nuclear binding energy
83  1.007825  83.649475 amu
125  1.008665  126.083125 amu
209.732600 amu
Dm  208.9804 amu - 209.732600 amu
Dm   0.7522 amu
1.00 kg


Dm   0.7522 amu  

26
 6.022  10 amu 
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Dm  1.24911027 kg

DE   1.249110
27

kg 3.00 10 m/s
8

2
DE   1.12  1010 kg m2 / s2
DE   1.12  10
10

J

DE   1.12  1010 J 6.022  1023 /mol

DE   6.74  1013 J/mol
DE   6.74  10 kJ/mol
13
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DE  - 6.74  1013 kJ/mol
Nuclear binding energy  6.74  1013 kJ/mol
b) Nuclear binding energy per nucleon
10
1.12  10 J
13
DE 
 5.38  10 J/nucleon
208 nucleons
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20.3 Natural Radioactivity
• The disintegration of a radioactive nucleus
often is the beginning of a radioactive
decay series, which is a sequence of
nuclear reactions that ultimately result in
the formation of a stable isotope.
• The beginning radioactive isotope is called
the parent and the product isotope is
called the daughter.
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Decay series for uranium-238
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• Kinetics of radioactive decay
– First-order kinetics (N – number of radioactive
nuclei at time t , k is the rate constant and t 1
/2
is the half-life)
rate of decay at time t  kN
Nt
ln
  kt
N0
0.693
t1/ 
2
k
– Used as the basis for dating (14C and 238 U
are used depending on material)
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A piece of linen cloth found at an ancient
burial site is found to have a 14C activity of
4.8 disintegrations per minute. Determine
the age of the cloth. Assume that the
carbon-14 activity of an equal mass of
living flax (the plant from which linen is
made) is 14.8 disintegrations per minute.
The half-life of carbon-14 is 5715 years.
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0.693
5715 years 
k
k  1.21104 yr -1
Nt
ln
  kt
N0
14
C activity in artifact
ln 14
  kt
C acitivity in living flax
4.8 d ps
4
1
ln
  1.12  10 yr t
14.8 dps
t  1.0  104 yr
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Uranium-238 Dating
Compare to ratio
found in sample.
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20.4 Nuclear Transmutation
• Nuclear transmutation differs from
radioactive decay in that transmutation is
brought about by the collision of two
particles.
• Particle accelerators made it possible to
synthesize the so-called transuranium
elements, elements with atomic numbers
greater than 92.
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Write an equation for the process represented by
106
46
Pd( , p)
109
47
Ag
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106
46
Pd( , p)109
47 Ag
bombarding particle
106
46
emitted particle
Pd  He 
4
2
109
47
Ag  p
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1
26
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Schematic diagram of a cyclotron particle accelerator.
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A particle accelerator uses electric and magnetic fields to
increase the kinetic energy of charged species so that a reaction
will occur.
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20.5 Nuclear Fission
• Nuclear fission is the process in which a
heavy nucleus (mass number > 200)
divides to form smaller nuclei of
intermediate mass and one or more
neutrons.
• Because the heavy nucleus is less stable
than its products, this process releases a
large amount of energy.
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• nuclear chain reaction, which is a selfsustaining sequence of nuclear fission
reactions.
• critical mass, the minimum mass of
fissionable material required to generate a
self-sustaining nuclear chain reaction.
• Applications of nuclear fission
– Atomic bomb
– Generation of electricity
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Critical Mass: Chain reaction occurs
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Schematic diagram of an atomic bomb
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Schematic Diagram of a Nuclear Fission Reactor
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Refueling the Core of a Nuclear Reactor
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• Types of reactors (Using
235
92
U as fuel)
– Light water reactor - uses H2O as
moderator used to reduce kinetic energy of
neutrons
– Heavy water reactor – uses D2O as
moderator
• More efficient than light water reactor
– Breeder reactor – produces more fissionable
fuel than it uses
• Doubling time – time to produce enough
fuel to refuel the original reactor
• Can utilize fertile isotopes plutonium-239
and thorium-232
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20.6 Nuclear Fusion
• Nuclear fusion - the combining of small nuclei
into larger one
– Exempt from waste disposal issues of fission
• Solar fusion
• Thermonuclear reactions – take place at very
high temperatures
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• Promising reactions
• Technical difficulty – confine nuclei at
required temperatures
– Magnetic confinement
– High-power lasers
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Tokamak : A magnetic plasma confinement design
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• Used in hydrogen (thermonuclear) bombs
– High temperatures attained
– Contain solid LiD
– Cleaner than fission bombs
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20.7 Use of Isotopes
• Chemical analysis
– Use of tracers
• Sulfur-35 in the determination of the
structure of thiosulfate
• Photosynthetic pathway using oxygen-18
and 14-carbon
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• Isotopes in medicine
– Use of tracers for diagnosis
• Sodium-24 – blood flow
• Iodine-131 –thyroid conditions
• Iodine -123 – brain imaging
normal
Alzheimer victim
– Major advantage – easy to detect
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Geiger Counter: Used to detect radiation
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20.8 Biological Effects of Radiation
• Quantitative measures of radation
– curie (Ci): fundamental unit of radioactivity
• Equivalent to 3.70 x 1010 nuclear
disintegrations per second
– rad (radiation absorbed dose)
• Considers activity
• Considers energy
• Considers type of radiation emitted
• 1 rad = 1 x 105 J/g of tissue irradiated
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– RBE (relative biological effectiveness)
• Considers biological effect of radiation
–Part of body irradiated
–Type of radiation
– rem (roentgen equivalent for man)
• Chemical basis for radiation damage
– Ionizing radiation produces radicals
– Radicals (free radicals) – molecular
fragments with unpaired electrons
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– e and the hydroxyl radical can form other
radicals
– In tissues radicals can attack and destroy
membranes, enzymes, DNA, etc.
• Radiation damage
– Somatic (affect the organism within its
lifetime)
– Genetic (inheritable changes and gene
mutations)
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Key Points
• Nuclei and nuclear reactions
– Radioactive decay
– Nuclear transmutations
– Particles involved in nuclear reactions
– Balancing nuclear reactions
• Nuclear stability
– Type of interactions involved
– Pattern of stability
• Magic numbers
• Odd/even numbers of nucleons
– Nuclear binding energy
• Mass defect
• Einstein’s mass-energy equivalence
relationship
• Calculation nuclear binding energy
–Per mole of nucleons
–Per nucleon
• Natural radioactivity
– Radioactive decay series
– Kinetics of radioactive decay
– Dating based on radioactive decay
• Carbon-14 dating
• Uranium-238 dating
• Potassium-40 dating
• Nuclear Transmutation
– Transuranium element
– Particle accelerators
• Nuclear fission
– Nuclear fission reactions
• Nuclear chain reactions
• Critical mass
– Generation of electric power
• Light water reactors
• Heavy water reactors
• Breeder reactors
– Nuclear fusion
• Solar nuclear reactions
• Thermonuclear reactions
• Potential for generation of electric power
• Thermonuclear bombs
• Uses of Isotopes
– Chemical Analysis
– Medicine
• Biological effects of radiation
– Units to measure radiation
• curie
• rad
• RBE
• rem
– Effect of free radicals
– Somatic damage
– Genetic damage