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Nuclear Chemistry
Chapter 23
23.1-23.6
Nuclear Chemistry
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Nuclear Chemistry- the study of reactions
involving changes in atomic nuclei.
Importance
Disadvantages
Nuclear Reactions
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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.
Nuclear Reactions
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Atomic number (Z) = number of protons in nucleus
Mass number (A) = number of protons + number of
neutrons
= atomic number (Z) + number of neutrons
Mass Number
Atomic Number
A
ZX
Element Symbol
Nuclear Reactions
neutron
1n
0
proton
1p
1H
or
1
1
positron
0
0
+1e or +1 b
electron
0b
0e
or
-1
-1
a particle
4He
4a
or
2
2
Balancing Nuclear Equations
1. 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
92 U
+ 10n
138
55 Cs
+
96
37 Rb
235 + 1 = 138 + 96 + 2x1
+ 2 10n
Balancing Nuclear Equations
2. 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.
235
92 U
+ 10n
138
55 Cs
+
96
37 Rb
92 + 0 = 55 + 37 + 2x0
+ 2 10n
Balancing Nuclear Equations
212Po
decays by alpha emission. Write the balanced
nuclear equation for the decay of 212Po.
4
alpha particle - 42He or 2a
212Po
84
4He
2
212 = 4 + A
A = 208
Z = 82
84 = 2 + Z
212Po
84
+ AZX
4He
2
+ 208
82Pb
Chemical Reactions vs. Nuclear
Reactions
Nuclear Stability
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Nucleus is very small
Contributes most of weight of atom
Extremely high density
Even higher # of particles
Nuclear Stability
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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.
n/p too large
beta decay
X
Y
n/p too small
positron decay or electron captur
Nuclear Stability
Beta decay
+-10b + n
14C
6
14N
7
40K
19
40Ca
20
+ -10b + n
1n
0
Decrease # of neutrons by 1
Increase # of protons by 1
1p
1
+ -10b + n
23.2
Nuclear Stability
Positron decay
++10b + n
11C
6
11B
5
38K
19
38Ar
18
Increase # of neutrons by 1
++10b + n
1p
1
Decrease # of protons by 1
1n
0
++10b + n
n and n have A = 0 and Z = 0
Nuclear Stability
Electron capture decay
+n
37Ar
18
+ -10e
37Cl
17
55Fe
26
+ -10e
55Mn
25
1p
1
+n
+ -10e
Increase # of neutrons by 1
Decrease # of protons by 1
1n
0
+n
Nuclear Stability
Alpha decay
212Po
84
4He
2
+ 208
82Pb
Decrease # of neutrons by 2
Decrease # of protons by 2
Nuclear Binding Energy
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Nuclear Binding Energy- the energy
required to break up a nucleus into its
component protons and neutrons.
Necessity?
Mass Defect
Einstein’s Theory of Relativity
E = mc2
Nuclear Binding Energy
BE + 199F
911p + 1010n
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
BE = 2.37 x 10-11J
1 amu = 1.49 x 10-10 J
Nuclear Binding Energy
binding energy
binding energy per nucleon =
number of nucleons
2.37 x 10-11 J
=
19 nucleons
= 1.25 x 10-12 J
Nuclear Binding Energy
Natural Radioactivity
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Outside the belt of stability, nuclei are
radioactive.
Radioactive nuclei spontaneously emit
radiation.
–
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α particles, β particles, γ rays, etc.
Disintegration of radioactive nucleus leads
to a decay series.
Radioactive Decay--Dating
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Uranium decay
After time, half of
parent exsists
Equal amounts of
parent and daughter
Age?
Nuclear Transmutations
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Rutherford, 1919
Artificial Radioactivity
Nitrogen bombarded by α particles
14N
7
+ 24a
17O
8
+ 11p
Nuclear Transmutation
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Notation for reactions
First Isotope (bombarding particle, ejected
particle) Final Isotope
Notation for Nitrogen-14 bombarded with a
particle.
Transuranium Elements
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Synthetic elements
Atomic Numbers greater than 92
Particle Accelerator necessary for
preparation
Particle Accelerator
Cyclotron Particle Accelerator
Nuclear Fission
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Nuclear Fission- the process in which a
heavy nucleus (mass number > 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.
Nuclear Fission
235U
92
+ 01n
90Sr
38
1n + Energy
+ 143
Xe
+
3
0
54
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.
Chain Reaction
Non-critical
Critical
The Atomic Bomb
Nuclear Reactors
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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
Light Water Reactors
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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
Light Water Reactors
Heavy Water Reactors
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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
Breeder Reactors
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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.
Hazards of Nuclear Energy
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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
Nuclear Fusion
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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.
Nuclear Fusion
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How do we get it to occur?
Container?
The Hydrogen Bomb
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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