NUCLEAR CHEMISTRY
Chapter 21 NUCLEAR CHEMISTRY
 Introduction
 The major energy source for our planet
• Essential to life on Earth.
• Provides ~1 kW/m2.
• Used by plants for photosynthesis that
produces food for plants and oxygen that most
life on Earth needs to survive.
 The energy of the Sun comes from the hydrogen
fusion reaction
 Nuclear chemistry is the study of nuclear
reactions
Chapter 21 NUCLEAR CHEMISTRY
 Nuclear Chemistry
 Used as therapeutic and diagnostic tools.
• Cobalt-60 for cancer therapy (gamma ray)
• Fluorine-18 for PET imaging
(positron)
• Thallium-201 for stress test
(gamma ray)
 Helps determine the
mechanisms of chemical
reactions
 Generates electricity
Chapter 21 NUCLEAR CHEMISTRY
 Introduction
Figure 21.1 Sources of electricity generation, worldwide and for select countries.
Chapter 21 NUCLEAR CHEMISTRY
 Nuclear Reactions
 Nuclear power
plants (provide 15%
of the total electricity
in the world)
Chapter 21 NUCLEAR CHEMISTRY
 Nuclear Reactions
국가별 원자력 전력생산량(2009)
Chapter 21 NUCLEAR CHEMISTRY
 The Nucleus
 Remember that the nucleus is comprised of
the two nucleons, protons and neutrons.
 The number of protons is the atomic number.
 The number of protons and neutrons together
is effectively the mass of the atom.
Chapter 21 NUCLEAR CHEMISTRY
 Isotopes
 Not all atoms of the same element have
the same mass due to different
numbers of neutrons in those atoms.
 There are, for example, three naturally
occurring isotopes of uranium:
234
• 92U Uranium-234, trace
• 235
92U Uranium-235, 0.7%
• 238
92U Uranium-238, 99.3%
Chapter 21.1 RADIOACTIVITY
 Radioactivity
A nuclide is a nucleus with a specified
number of protons and neutrons
 It is not uncommon for some nuclides of
an element to be unstable, or
radioactive.
 We refer to these as radionuclides.
 There are several ways radionuclides
can decay into a different nuclide.
Chapter 21.1 RADIOACTIVITY
 Types of Radioactive Decay
 Alpha decay
 Beta decay
 Positron emission
 Gamma decay
 Electron capture
Chapter 21.1 RADIOACTIVITY
 Alpha Decay
 -decay is the loss of an -particle
(a helium nucleus)
4
2
238
92
U

He
234
90
Th + He
4
2
Thorium
This expression is called nuclear equation
Chapter 21.1 RADIOACTIVITY
 Beta Decay
 -decay is the loss of a -particle
(a high energy electron).
0
−1
131
53
I


or
131
54
0
−1
e
Xe
+
0
−1
e
Chapter 21.1 RADIOACTIVITY
 Positron Emission
 Some nuclei decay by emitting a positron,
a particle that has the same mass as but
an opposite charge to that of an electron.
0
1
11
6
C

e
11
5
B
+
0
1
e
Chapter 21.1 RADIOACTIVITY
 Electron Capture
 Addition of an electron to a proton
in the nucleus is known as electron
capture.
• The result of this process is that a
proton is transformed into a
neutron.
p+ e
1
0
1
−1

n
1
0
Chapter 21.1 RADIOACTIVITY
 Gamma Emission
 This is the loss of a -ray, which is highenergy radiation that accompanies the
loss of a nuclear particle.
0
0

Chapter 21.2 PATTERNS OF NUCLEAR STABILITY
 Patterns of Nuclear Stability
 Any element with more than one proton (i.e.,
anything but hydrogen) will have repulsions
between the protons in the nucleus
 A strong nuclear force helps keep the nucleus from
flying apart
 Neutrons play a key role stabilizing the nucleus
 Therefore, the ratio of neutrons to protons is an
important factor
Chapter 21.2 PATTERNS OF NUCLEAR STABILITY
 Neutron-Proton Ratios
 For smaller nuclei (Z  20),
stable nuclei have a
neutron-to-proton ratio
close to 1:1.
Figure 21.2 Stable and radioactive isotopes as
a function of numbers of neutrons and protons
in a nucleus.
Chapter 21.2 PATTERNS OF NUCLEAR STABILITY
 Neutron-Proton Ratios
 As nuclei get larger, it takes
a greater number of
neutrons to stabilize the
nucleus.
Figure 21.2 Stable and radioactive isotopes as
a function of numbers of neutrons and protons
in a nucleus.
Chapter 21.2 PATTERNS OF NUCLEAR STABILITY
 Stable Nuclei
 The black-dotted region in
the figure represent stable,
nonradioactive isotopes.
Figure 21.2 Stable and radioactive isotopes as
a function of numbers of neutrons and protons
in a nucleus.
Chapter 21.2 PATTERNS OF NUCLEAR STABILITY
 Stable Nuclei
 Nuclei above this
belt have too many
neutrons.
 They tend to decay
by emitting beta
particles.
Chapter 21.2 PATTERNS OF NUCLEAR STABILITY
 Stable Nuclei
 Nuclei below the
belt have too many
protons.
 They tend to
become more
stable by positron
emission or electron
capture.
Chapter 21.2 PATTERNS OF NUCLEAR STABILITY
 Stable Nuclei
 There are no stable nuclei
with an atomic number
greater than 83.
 Nuclei with such large
atomic numbers tend to
decay by alpha emission.
 For example, all isotopes
of uranium, atomic
number 92, are
radioactive.
Chapter 21.2 PATTERNS OF NUCLEAR STABILITY
 Radioactive Series
 Large radioactive
nuclei cannot stabilize
by undergoing only one
nuclear transformation.
 They undergo a series
of decays until they
form a stable nuclide
(often a nuclide of lead).
Figure 21.3 Nuclear disintegration series for uranium-238.
Chapter 21.2 PATTERNS OF NUCLEAR STABILITY
 Further Observations
 Nuclei with 2, 8, 20, 28, 50, or 82 protons or 2, 8,
20, 28, 50, 82, or 126 neutrons tend to be more
stable than nuclides with a different number of
nucleons.
(the shell model of the nucleus, magic numbers)
 Nuclei with an even
number of protons and
neutrons tend to be
more stable than
nuclides that have odd
numbers of these
nucleons.
Chapter 21.2 PATTERNS OF NUCLEAR STABILITY
 Further Observations
Figure 21.4 Number of stable isotopes for elements 1–54.
Chapter 21.3 NUCLEAR TRANSMUTATIONS
 Nuclear Transmutations
 In 1919, Ernest Rutherford
performed the first
conversion of one nucleus
into another.
 Nuclear transmutations can
be induced by accelerating
a particle and colliding it
with the nuclide.
Chapter 21.3 NUCLEAR TRANSMUTATIONS
 Particle Accelerators
 These particle accelerators are enormous,
having circular tracks with radii that are
miles long.
Figure 21.5 The Relativistic
Heavy Ion Collider. This
particle accelerator is
located at Brookhaven
National Lab on Long Island,
New York.
Chapter 21.3 NUCLEAR TRANSMUTATIONS
 Using Neutrons
 Because Neutrons are neutral, they are not repelled
by the nucleus. (acceleration is not required)
(radioactive)
 Transuranium Elements
 Artificial transformations have been used to produce
the elements with atomic number above 92.
2009, Prentice-Hall, Inc.
Chapter 21.4 RATES OF RADIOACTIVE DECAY
 Rates of Radioactive Decay
 Unaffected by external
conditions such as
temperature, pressure or
state of chemical combination.
Figure 21.6 Decay of a
10.0-g sample of Sr-90 (t1/2
= 28.8 yr).
Chapter 21.4 RATES OF RADIOACTIVE DECAY
 Radiometric Dating
 The half life can serve as a nuclear clock to
determine the ages of different objects.
 A living plant or animal is able to maintain a
ratio of 14C to 12C that is nearly identical with
that of the atmosphere.
 Once the organism dies, the ratio of 14C to 12C
decreases.
 The t1/2 of 14C is 5715 yr.
Formation:
Decay:
Chapter 21.4 RATES OF RADIOACTIVE DECAY
 Radiometric Dating
Figure 21.7
Creation and
distribution of 14C.
The ratio of 14C to 12C in
a dead animal or plant is
related to the time since
death occurred.
Chapter 21.4 RATES OF RADIOACTIVE DECAY
 Kinetics of Radioactive Decay
 Nuclear transmutation is a first-order
process.
k is the first order rate constant
N is the number of radioactive nuclei
 The kinetics of such a process, you will
recall, obey this equation:
(a)
(b)
(c) One Bq is defined as one nuclear disintegration per second.
1 Ci = 3.7 X 1010 Bq
Chapter 21.5 DETECTION OF RADIOACTIVITY
 Measuring Radioactivity
 A variety of methods have been devised to detect
emissions from radioactive substances
Figure 21.8 Badge dosimeters monitor the extent to which
the individual has been exposed to high-energy radiation.
Chapter 21.5 DETECTION OF RADIOACTIVITY
 Measuring Radioactivity
 One can use a device like this Geiger counter to
measure the amount of activity present in a
radioactive sample.
 The ionizing radiation creates ions, which conduct
a current that is detected by the instrument.
Chapter 21.5 DETECTION OF RADIOACTIVITY
 Measuring Radioactivity
 Phosphors
• Substances excited by
radiation can also be used to
detect and measure radiation.
 Scintillation counter
• Detects the tiny flashes of
light produced when radiation
strikes a suitable phosphor.
Chapter 21.5 DETECTION OF RADIOACTIVITY
 Measuring Radioactivity
 Photographic plates
or film.
Chapter 21.5 DETECTION OF RADIOACTIVITY
 Radiotracers
 How can you prove that plants use CO2
to produce glucose by photosynthesis?
 What about the source of the oxygen in
O 2?
Chapter 21.5 DETECTION OF RADIOACTIVITY
 Radiotracers
FDG, fluorodeoxyglucose
18F,
t1/2=110min
Chapter 21.5 DETECTION OF RADIOACTIVITY
 Radiotracers
Figure 21.10 Schematic
representation of a positron emission
tomography (PET) scanner.
Figure 21.11 Positron emission
tomography (PET) scans showing
glucose metabolism levels in the brain.
Red and yellow colors show higher
levels of glucose metabolism.
Chapter 21.6 ENERGY CHANGES IN NUCLEAR REACTIONS
 Nuclear Energy
• There is a tremendous amount of energy stored
in nuclei.
• Einstein’s famous equation, E = mc2, relates
directly to the calculation of this energy.
• In the types of chemical reactions we have
encountered previously, the amount of mass
converted to energy has been minimal.
• However, these energies are many thousands of
times greater in nuclear reactions.
Chapter 21.6 ENERGY CHANGES IN NUCLEAR REACTIONS
 Energy in Nuclear Reactions
 For example, the mass change for the decay of 1
mol of uranium-238 is −0.0046 g.
 The change in energy, E, is then
E = (m) c2
E = (−4.6  10−6 kg)(3.00  108 m/s)2
E = −4.1  1011 J
Chapter 21.6 ENERGY CHANGES IN NUCLEAR REACTIONS
 Nuclear Binding Energy
 The mass difference between a nucleus and its constituent
nucleons is called the mass defect
 The energy required to separate a nucleus into its individual
nucleons is called the nuclear binding energy
Chapter 21.6 ENERGY CHANGES IN NUCLEAR REACTIONS
 Nuclear Binding Energy
 The energy required to
separate a nucleus into
its individual nucleons
Figure 21.12 Nuclear binding
energies. The average binding
energy per nucleon increases initially
as the mass number increases and
then decreases slowly. Because of
these trends, fusion of light nuclei
and fission of heavy nuclei are
exothermic processes.
Chapter 21.7 NUCLEAR POWER: FISSION
 Nuclear Fission
 Nuclear fission is the type of reaction carried out
in nuclear reactors
 It is an exothermic process
13
Chapter 21.7 NUCLEAR POWER: FISSION
 Nuclear Fission
14
 Bombardment of the radioactive nuclide with a
neutron starts the process.
 Neutrons released in the transmutation strike
other nuclei, causing their decay and the
production of more neutrons.
Chapter 21.7 NUCLEAR POWER: FISSION
 Nuclear Fission
14
 This process continues in what we call a nuclear
chain reaction
 If there are not enough radioactive nuclides in the
path of the ejected neutrons, the chain reaction
will die out
Chapter 21.7 NUCLEAR POWER: FISSION
 Nuclear Fission
15
 Therefore, there must be a certain minimum
amount of fissionable material present for the
chain reaction to be sustained: critical mass.
Chapter 21.7 NUCLEAR POWER: FISSION
 Nuclear Fission
 To trigger a fission reaction,
two subcritical masses of
uranium-235 are slammed
together using chemical
explosives
16
Chapter 21.7 NUCLEAR POWER: FISSION
 Nuclear Fission
Chapter 21.7 NUCLEAR POWER: FISSION
 Nuclear Reactors
 Nuclear fission produces
the energy generated by
nuclear power plants
 Control rods block the
paths of some neutrons
and regulate the flux of
neutrons to prevent the
reactor core from
overheating
16
Chapter 21.7 NUCLEAR POWER: FISSION
 Nuclear Reactors
 In nuclear reactors the heat generated by the
reaction is used to produce steam that turns a
turbine connected to a generator.
Figure 21.19 Basic design of a pressurized water reactor nuclear power plant.
Chapter 21.7 NUCLEAR POWER: FISSION
 Nuclear waste
 Disposal of spent nuclear fuel poses a major problem in
nuclear power
 The most attractive possibilities appear to be formation of
solid materials from the wastes and bury them deep ground
in containers of high corrosion resistance and durability
Chapter 21.8 NUCLEAR POWER: FUSION
 Nuclear Fusion
 The Sun is composed of 73% H, 26%, He, and other
elements.
 Fusion would be a superior method of generating
power.
• The products of the reaction are not radioactive.
• In order to achieve fusion, the material must be in the
plasma state at several million kelvins – not practical
Requires 40,000,000 K.
Chapter 21.9 RADIATION IN THE ENVIRONMENT AND LIVING SYSTEMS
 Radiations around us





Radiation from the Sun
Radio waves from radio and TV
Microwaves from microwave ovens
X-rays from various medical procedures
Radiation from the soil and other natural materials
Chapter 21.9 RADIATION IN THE ENVIRONMENT AND LIVING SYSTEMS
 Ionization Radiation
 Radiation causing ionization (Ionizing radiation)
is harmful to biological systems
 Alpha, beta, and gamma rays/X-rays and higher
energy UV radiation can ionize water to form
H2O+
Free radical
Unstable
Highly reactive
Chapter 21.8 RADIATION IN THE ENVIRONMENT AND LIVING SYSTEMS
 Effects of Radiation
Figure 21.25
Sources of U.S. average
annual exposure to highenergy radiation.
The total average annual
exposure is 360 mrem.
Chapter 21.8 RADIATION IN THE ENVIRONMENT AND LIVING SYSTEMS
 Radon
 Radon-222 is a product of the
nuclear disintegration series of
uranium-238.
 Radon exposure accounts for more
than half of the annual exposure.
 A noble gas and readily inhaled.
 Short half life
 Contributes to 10% of all lung cancer
death.
Half life = 3.82 days
Half life = 3.11 min
Chapter 21.8 RADIATION IN THE ENVIRONMENT AND LIVING SYSTEMS
 Radon
Figure 21.26 EPA map of radon zones in the United States.
Chapter 21.8 RADIATION IN THE ENVIRONMENT AND LIVING SYSTEMS
 Radiation Therapy
 Malignant tumors can be destroyed by exposing
them to the same radiation that caused them.
 Mostly radiation therapy uses the high-energy
gamma radiation.
M.W. 74.55
M.W. 74.55
21.69
21.77
21.84