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12/27/16
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Ch. 21: Nuclear Chemistry
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Nuclear chemistry provides the basis for many useful diagnostic and therapeutic methods
in medicine, such as these positron emission tomography (PET) scans. The PET/computed
tomography scan on the left shows muscle activity. The brain scans in the center show
chemical differences in dopamine signaling in the brains of addicts and nonaddicts.
The images on the right show an oncological application of PET scans to identify
lymph node metastasis.
Chemistry: OpenStax
!  Nuclear (NOT Nucular) chemistry involves changes
in the nuclear composition (protons and neutrons) of
atoms that are radioactive.
X
!  Nuclear chemistry can be used:
Atomic number (Z) = number of protons
Mass number (A) = number of protons and neutrons in a
specific isotope (or nuclide) of an element
!  for radiocarbon dating (e.g., determining the age of a
mummy or a meteorite)
!  for medical diagnosis and treatment
!  for medical imaging (PET scans, brain scans, x-rays)
!  in nuclear power plants
!  to create new elements
Protons and neutrons are collectively called nucleons.
How many neutrons are in each isotope?
C
13
6
C
14
6
C
2
Nuclear Reactions
Spontaneous emission of particles or electromagnetic radiation is
known as radioactivity.
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http://2012books.lardbucket.org/pdfs/principles-of-generalchemistry-v1.0.pdf
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Nuclei and Nuclear Reactions
A
Atomic notation and terms: Z
!  Principles of General Chemistry (CC BY-NC-SA 3.0):
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3
21.1 Nuclear Structure and Stability
How do we know whether an isotope is
stable? Which radioisotopes will
spontaneously decay?
1)  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.
2)  Even numbers of protons and neutrons
tend to be stable.
3)  All isotopes of the elements with
atomic numbers > 83 are radioactive.
4)  All isotopes of technetium (Tc, Z = 43)
and promethium (Pm, Z = 61) are
radioactive.
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Components_of_the_Nucleus
Band of Stability
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Components_of_the_Nucleus
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Predicting Types of Decay
The three general classes of radioactive nuclei are characterized by a different
decay process or set of processes:
Neutron-rich nuclei. The nuclei on the upper left side of the band of stable
nuclei in Figure 18.1.2 have a neutron-to-proton ratio that is too high to give a
stable nucleus. These nuclei decay by a beta decay – converting a neutron to a
proton, thereby decreasing the neutron-to-proton ratio.
Predicting
Types of
Decay
Neutron-poor nuclei. Nuclei on the lower right side of the band of stable
nuclei have a neutron-to-proton ratio that is too low to give a stable nucleus.
These nuclei decay by positron emission or electron capture - converting a
proton to a neutron, thereby increasing the neutron-to-proton ratio.
Heavy nuclei. With very few exceptions, heavy nuclei (those with A ≥ 200) are
intrinsically unstable regardless of the neutron-to-proton ratio, and all nuclei
with Z > 83 are unstable. Such nuclei tend to decay by emitting an α particle
which decreases the number of protons and neutrons in the original nucleus by
2. The net result of alpha emission is an increase in the neutron-to-proton ratio.
https://en.wikipedia.org/wiki/Radioactive_decay#Types_of_decay
Penetrating Ability of Particles
21.2 Nuclear Equations
Figure 21.4: Symbols for subatomic particles
Figure 21.33
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Types of Nuclear Reactions
Figure 21.7: Types of Nuclear Decay
• 
Radioactive decay/emission: an unstable nuclide emits a
particle or energy.
•  Parent nuclide ! daughter nuclide + radiation
212
208
+ 42 He
84 Po
82 Pb
• 
Fission: bombarding an isotope with a neutron to break it apart
into lighter isotopes.
Fusion: light isotopes collide to form heavier isotopes (only up
to Fe can be done naturally in the universe)
Transmutation: atoms are bombarded by high energy particles
to create new elements/isotopes.
14N + 4He " 17O + 1H
• 
"
"
"
• 
• 
"
"
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12
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21.3 Radioactive Decay
Alpha Decay (or Emission)
In balancing a nuclear reaction, we balance the total of all
atomic numbers and total of all mass numbers for the
products and reactants (conservation of protons and
neutrons).
Mass number:
212
212
84
Atomic number:
Po
!  Alpha decay - heavy radioisotopes tend to emit alpha
particles (A dec. by 4, Z dec by 2)
!  238U " 4He + 234Th
208 + 4 = 212
208
82
84
Pb
+
4
2
He
!  Predict products:
82 + 2 = 84
Example 21.4
13
226Ra
" 4He + X
244Pu
" 4He + X
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http://underground.physics.berkeley.edu/SNO+.html
Beta Decay (or Emission)
Gamma Decay (or Emission)
!  Beta decay - neutron is converted to a proton and an
!  Gamma – γ: energy with no mass or charge; the most
electron (A is same, Z inc. by 1)
penetrating radiation (A and Z remain the same)
!  14C " 14N + e-
!  This often occurs in conjunction with alpha or beta
decay.
!  60*Co " 60Ni + e- + γ
!  Predict products:
!  239U " X + ehttp://www.ck12.org/user:chjpdgnoyxjkx3naagnkzs5vcmc./book/Chemical-Equations-and-Balancing-TheEquations/section/24.2/
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Positron Decay (or Emission)
http://2012books.lardbucket.org/books/principles-of-general-chemistry-v1.0/s24nuclear-chemistry.html
Electron Capture
!  Electron Capture – electron combines with a
!  Positron decay – proton is converted to a neutron
and an electron (A is same, Z dec. by 1)
proton to form a neutron (A is same, Z dec by 1)
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Same result as Positron Emission; Opposite of Beta
Emission 81 Kr + 0 e → 81 Br + 0γ
23
11
Mg → Na +
0
+1
0
0
e+ γ
36
-1
35
0
!  Predict products:
!  197Hg + e- " X
!  Predict products:
!  207Po " X + +10 e
http://2012books.lardbucket.org/books/principles-of-general-chemistry-v1.0/s24nuclear-chemistry.html
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http://2012books.lardbucket.org/books/principles-of-general-chemistry-v1.0/s24nuclear-chemistry.html
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Group Work - Practice
!  Write balanced equations for the following:
!  Alpha decay of curium-242
(238Pu)
!  Beta decay of magnesium-28
Determining Products of Reactions
Nuclear Transmutation:
249
98
48
Cf + 20
Ca → X + 3 01 n
Natural radioactive decay:
(28Al)
238
92
!  Positron emission from xenon-118
U → X + 8 24α + 6 -10 β
Nuclear fission:
(118I)
!  Electron capture by polonium-204
235
92
(204Bi)
U +
1
0
n → X +
143
54
Xe + 3 01 n
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https://en.wikipedia.org/wiki/Full_body_scanner
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Radioactive Decay Series
Uranium Series of Decay
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. 232Th " 208Tl
Decay calculations help us
determine how long radioactive
waste has to be stored. Typically 10
half-lives: 2-10 = 0.000977 (so
99.9023% has decayed)
http://commons.wikimedia.org/wiki/User:BatesIsBack - http://commons.wikimedia.org/
wiki/File:Decay_Chain_of_Thorium.svg, CC BY-SA 3.0, https://commons.wikimedia.org/
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w/index.php?curid=16983885
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162/21%3A_Nuclear_Chemistry/21.1%3A_Radioactivity
Four New Elements!
https://www.sciencenews.org/article/four-elements-earnpermanent-seats-periodic-table
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Uses of Radioactive Isotopes
! 
! 
! 
! 
! 
! 
! 
! 
! 
! 
Prostate Cancer: yttrium-90
Bones: calcium-47 (also phosphorus)
Positron-emission tomography (PET scans): carbon-11
Leukemia: actinium-225
Spleens: iron-59
Arteries: rhenium-188
Arthritis: erbium-169
Liver: cobalt
Thyroid: iodine
Technetium-99: tumors and imaging brain, lungs, liver,
skeleton, and blood
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Annual Radiation Exposure
Symptoms of Exposure
Dose
(rem)
Symptoms/Effects
<5
No observable effect
5-20
Possible chromosomal damage
20-100
Temporary reduction in white blood cell count
50-100
Temporary sterility in men (up to a year)
100-200 Mild radiation sickness, vomiting, diarrhea, fatigue; immune
system suppressed; bone growth in children retarded
Figure 21.37: The total annual radiation exposure for a person in the US is
about 620 mrem. The various sources and their relative amounts are shown
in this bar graph. (source: U.S. Nuclear Regulatory Commission)
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Nuclear Decay – Half-Lives
> 300
Permanent sterility in women
> 500
Fatal to 50% within 30 days; destruction of bone marro and
intestine
> 3000
Fatal within hours
http://2012books.lardbucket.org/books/principles-of-general-chemistry-v1.0/s24nuclear-chemistry.html
First Order Decay
!  The rate of decay, as well as the type and energy
of the radiation, determines the damage caused by
radiation.
!  Nuclear decay follows first-order kinetics, which
gives a constant t1/2 over the course of the decay.
!  Typically we are given half-life (t1/2) values. We
can use these to calculate rate constants (or decay
constants) for radioactive nuclides.
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Nuclear Radioactivity
Nuclear Decay - Kinetics
!  Can use kinetics equations, just like in Chapter 12,
All radioactive decays obey first-order kinetics.
N
ln t = - kt
N0
Half-life is the time it takes for the amount of a substance
to decrease by 50%.
The corresponding half-life of the reaction is given by:
t1 =
2
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0.693
k
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to perform calculations:
!  How much nuclide (mass or %) is left after ___
time?
!  How long does it take for ___% to decay (or
remain)?
!  The half-life for sodium-24, a radioisotope used
medically in blood studies, is 906 minutes. What is
the rate constant for 24Na (in hr-1)?
!  4.59 x 10-2 hr-1
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Informative/Interesting Links
Group Work
Video about fallout from Chernobyl(46 min.):
http://www.youtube.com/watch?v=GezeZlu70oI
!  If you ingest a 75.0 mg sample of 131I with a rate
constant of 0.0861 d-1, how long would it take to decay
to 12.5 mg?
!  20.8 days
!  Gold-128 undergoes beta decay to give mercury-128
Fermi and the “Atomic Pile”:
http://www.fi.edu/learn/case-files/fermi/pile.html
with a half-life of 2.7 days. If you start with 5.6 mg of
128Au, what mass of gold-128 is left after 9.5 days?
!  0.49 mg
Distribution and history of energy sources:
http://www.world-nuclear.org/info/Current-and-Future-Generation/
Nuclear-Power-in-the-World-Today/#.Uebm_ZyETLc
!  226Ra has a half-life of 1620 years. Calculate the rate
constant and what percent of a sample would remain
after 100 years.
!  4.28 x 10-4 yr-1; 95.8% remains
!  Examples 21.5 – 21.7
10 Interesting Facts about Chernobyl:
http://imgur.com/gallery/AfbNLQ9
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Global Energy Sources
How geological dating on rocks is done:
http://www.youtube.com/watch?v=1920gi3swe4
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World Energy Consumption
http://www.world-nuclear.org/info/inf01.html
http://www.nucleartourist.com/basics/why.htm
!  List of advantages/disadvantages
of each energy source.
https://en.wikipedia.org/wiki/Renewable_energy#/media/File:Total_World_Energy_
Consumption_by_Source_2013.png
Nuclear Energy
21.4 Nuclear Transmutation
Schematic of a cyclotron particle accelerator.
!  Energy released from 200 g U = 2x1013 J
!  Energy released from 1 ton coal = 5x107 J
!  It would take 1 million tons of coal to create the
same amount of energy.
!  Nuclear power plants don’t explode (like TNT)
unless an uncontrolled nuclear chain reaction occurs.
When nuclear power plants have meltdowns, the
threat is from leakage of radioactive material (water,
airborne, soil contamination, etc.)
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http://www.physbot.co.uk/magnetic-fields-and-induction.html
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Transmutation
Transmutation
Nuclear transmutation differs from radioactive decay in
that transmutation is brought about by the collision of two
particles.
1
14
4
17
p
7 N + 2α
8O + 1
Particle accelerators made it possible to synthesize the socalled transuranium elements, elements with atomic
numbers greater than 92.
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A Linear Particle Accelerator. (a) An aerial view of the SLAC, the longest linear
particle accelerator in the world; the overall length of the tunnel is 2 miles. (b)
Rapidly reversing the polarity of the electrodes in the tube causes the charged
particles to be alternately attracted as they enter one section of the tube and repelled
as they leave that section. As a result, the particles are continuously accelerated
along the length of the tube.
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Nuclear Fission
Nuclear Fission
Nuclear fission: heavy nuclei (mass number > 200) are
bombarded by neutrons to form smaller nuclei and one or more
neutrons. Used in nuclear power plants.
235
92
141
U + 01 n → 236
92 U → 56 Ba +
92
36
Kr + 3 01 n
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Nuclear Fission
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235U
is capable of a self-sustaining sequence of nuclear fission
known as a nuclear chain reaction. The minimum mass of
material required to generate a self-sustaining chain reaction is the
critical mass.
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Components_of_the_Nucleus
youtube video
21.5 Archeological Dating
C -14 Dating:
http://www.youtube.com/watch?v=81dWTeregEA&feature=related
!  The decay of radioactive isotopes allows for the
relative age of once-living things to be calculated.
!  Radiocarbon dating uses 14C
!  Living things have a dynamic equilibrium of 14C
in their system (ex: inhaling/exhaling)
(a) The Diablo Canyon Nuclear Power Plant near San Luis Obispo is the only nuclear power
plant currently in operation in California. The domes are the containment structures for the
nuclear reactors, and the brown building houses the turbine where electricity is generated.
Ocean water is used for cooling. (b) The Diablo Canyon uses a pressurized water reactor, one
of a few different fission reactor designs in use around the world, to produce electricity.
Energy from the nuclear fission reactions in the core heats water in a closed, pressurized
system. Heat from this system produces steam that drives a turbine, which in turn produces
electricity. (credit a: modification of work by “Mike” Michael L. Baird; credit b: modification
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of work by the Nuclear Regulatory Commission)
162/21%3A_Nuclear_Chemistry/21.1%3A_Radioactivity
!  When a plant or animal dies, it no longer
incorporates new 14C, and the 14C begins to decay,
causing the 14C content to become less than that in
the atmosphere.
! 
14
6C
" 147N + 0-1e-
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Geological Dating
Radiometric Dating:
Well-Known Incidents
http://www.youtube.com/watch?v=1920gi3swe4
!  Three-Mile Island (Pennsylvania, 1979): Caused by
mechanical failures; small radiation leak (not linked to a
cancer fatality, no observable long term health effects).
!  Geological dating is similar to archeological dating,
but uses longer-lived nuclides
!  Measure ratio of 40K to 40Ar in rocks
!  4019K + 0-1e " 4018Ar
!  Chernobyl (Ukraine, 1986): No containment, 31 deaths
attributed to accident, radiation leak caused health issues
(50,000 excess cancer cases).
!  4019K " 4020Ca + 0-1e
!  40K has a half-life of 1.28x109 years
!  Rocks are crushed, 40Ar escapes, and the ratio of 40K
to 40Ar is measured.
!  This allowed the age of the earth to be calculated to
be 4.5 billion years.
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!  Fukushima, Japan (March 2011): Not caused by
earthquake – low-lying generators flooded from tsunami;
seawater to cool down reactors used too late. Singlereplacement reaction produced hydrogen gas causing
several chemical explosions. Radioactivity release about
1/10 of Chernobyl.
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Nuclear Fusion
Nuclear Fusion
Nuclear fusion is the process of combining small nuclei
into larger ones (up to 59Fe). Because fusion reactions take
place at very high temperatures, they are often called
thermonuclear reactions.
ITER: France – building the Tokamak, a device that uses
magnetic fields to contain and control hot plasma needed
for fusion. 2
3
4
1
1
D + 1T → 2 He + 0 n + 17.6 MeV
Due to the high temperature
requirements, containment
is an issue.
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Components_of_the_Nucleus
21.5 Uses of Isotopes
https://en.wikipedia.org/wiki/Tokamak_Fusion_Test_Reactor
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21.6 Biological Effects of Radiation
The fundamental unit of radioactivity is the curie (Ci)
Radioactive and stable isotopes have
applications in science and medicine.
1 Ci = 3.70 x 1010 disintegrations per second.
Radioactive isotopes are used as
tracers.
Use of tracers for diagnosis include:
! Sodium-24 – blood flow
! Iodine-131 – thyroid conditions
! Iodine-123 – brain imaging
https://en.wikipedia.org/wiki/Brain_positron_emission_tomography
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https://en.wikipedia.org/wiki/Geiger_counter
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Biological Effects of Radiation
A common unit for the absorbed dose of radiation is the
rad (radiation absorbed dose).
1 rad = 1 x 10-5 J/g of tissue irradiated
The rem (roentgen equivalent for man) is determined from
the number of rads:
Number of rems = number of rads x 1 RBE
RBE = the relative biological effectivness.
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