Fundamentals of General,
Organic, and Biological Chemistry
5th Edition
Chapter Eleven
Nuclear Chemistry
James E Mayhugh
Oklahoma City University
2007 Prentice Hall, Inc.
Outline
► 11.1 Nuclear Reactions
► 11.2 The Discovery and Nature of Radioactivity
► 11.3 Stable and Unstable Isotopes
► 11.4 Nuclear Decay
► 11.5 Radioactive Half-Life
► 11.6 Radioactive Decay Series
► 11.7 Ionizing Radiation
► 11.8 Detecting Radiation
► 11.9 Measuring Radiation
► 11.10 Artificial Transmutation
► 11.11 Nuclear Fission and Nuclear Fusion
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11.1 Nuclear Reactions
► The atomic number, written below and to the left of
the element symbol, gives the number of protons in
the nucleus and identifies the element.
► The mass number, written above and to the left of the
element symbol, gives the total number of nucleons, a
general term for both protons (p) and neutrons (n).
► The most common isotope of carbon, for example,
has 12 nucleons: 6 protons and 6 neutrons:
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► Nuclear reaction: A reaction that changes an atomic
nucleus, usually causing the change of one element
into another. A chemical reaction never changes the
nucleus.
► Different isotopes of an element have essentially the
same behavior in chemical reactions but often have
completely different behavior in nuclear reactions.
► The rate of a nuclear reaction is unaffected by a
change in temperature or pressure (within the range
found on Earth) or by the addition of a catalyst.
► The nuclear reaction of an atom is essentially the
same whether it is in a chemical compound or in an
uncombined, elemental form.
► The energy change accompanying a nuclear reaction
can be up to several million times greater than that
accompanying a chemical reaction.
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11.2 The Discovery and Nature of
Radioactivity
► In 1896, the French physicist Henri Becquerel
noticed a uranium-containing mineral exposed a
photographic plate that had been wrapped in paper.
► Marie and Pierre Curie investigated this new
phenomenon, which they termed radioactivity: The
spontaneous emission of radiation from a nucleus.
► Ernest Rutherford established that there were at least
two types of radiation, which he named alpha and
beta. Shortly thereafter, a third type of radiation was
found and named for the third Greek letter, gamma.
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When passed between two charged plates:
► Alpha rays, helium nuclei (He+2), bend toward the
negative plate because they have a positive charge.
► Beta rays, electrons (e-), bend toward the positive
plate because they have a negative charge.
► Gamma rays, photons (g), do not bend toward either
plate because they have no charge.
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►Alpha rays move about ~0.1c and can be stopped by
a few sheets of paper or by the top layer of skin.
►Beta rays move at up to 0.9c and have about 100
times the penetrating power of a particles. A block of
wood or heavy clothing is necessary to stop b rays.
►Gamma rays move at c and have about 1000 times the
penetrating power of a rays. A lead block several
inches thick is needed to stop g rays.
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11.3 Stable and Unstable Isotopes
►Every element in the periodic table has at least one
radioactive isotope, or radioisotope, and more than
3300 radioisotopes are known.
►Their radioactivity is the result of having unstable
nuclei, although the exact causes of this instability are
not fully understood. Radiation is emitted when an
unstable radioactive nucleus, or radionuclide,
spontaneously changes into a more stable one.
►There are only 264 stable isotopes among all the
elements.
►All isotopes of elements with atomic numbers higher
than that of bismuth (83) are radioactive.
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►For elements in the first
few rows of the periodic
table, stability is
associated with a roughly
equal number of neutrons
and protons.
►As elements get heavier,
the number of neutrons
relative to protons in
stable nuclei increases.
►Lead-208, for example,
the most abundant stable
isotope of lead, has 126
neutrons and 82 protons in
its nuclei.
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11.4 Nuclear Decay
► Nuclear decay: The spontaneous emission of a
particle from an unstable nucleus.
► Transmutation: The change of one element into
another.
► The equation for a nuclear reaction is not balanced in
the usual chemical sense because the kinds of atoms
are not the same on both sides of the arrow. A
nuclear equation is balanced when the number of
nucleons and the sums of the charges are the same on
both sides.
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► During alpha emission, the nucleus loses two protons
and two neutrons.
► Emission of an a particle from an atom of uranium-238
produces an atom of thorium-234.
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► Beta emission involves the decomposition of a
neutron to yield an electron and a proton.
► Iodine-131, a radioisotope used in detecting thyroid
problems, undergoes nuclear decay by b emission to
yield xenon-131.
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► Positron emission involves the conversion of a proton
in the nucleus into a neutron plus an ejected positron.
► A positron has the same mass as an electron but a
positive charge.
► Potassium-40 undergoes positron emission to yield
argon-40.
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► Electron capture, symbolized E.C., is a process in
which the nucleus captures an inner-shell electron
from the surrounding electron cloud, thereby
converting a proton into a neutron.
► The conversion of mercury- 197 into gold-197 is an
example of electron capture.
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► Emission of g rays causes no change in mass or
atomic number.
► g emission usually accompanies emission of other
rays but it is often omitted from nuclear equations.
► Their penetrating power makes them both dangerous
to humans and useful in medical applications.
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11.5 Radioactive Half-Life
► Rates of nuclear decay are measured in units of halflife, defined as the amount of time required for onehalf of the radioactive sample to decay.
► Each passage of a half-life causes the decay of one
half of whatever sample remains. The half-life is the
same no matter what the size of the sample, the
temperature, or any other external conditions.
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All nuclear decays follow the same curve, 50% of the
sample remains after one half-life, 25% after two
half-lives, 12.5% after three half-lives, and so on.
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Radioisotopes used internally for medical applications
have short half-lives so that they decay rapidly and do
not remain in the body for prolonged periods.
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11.6 Radioactive Decay Series
►Decay series: A
series of nuclear
disintegrations
leading from a heavy
radioisotope to a
nonradioactive
product.
►Uranium-238, for
example, undergoes
a series of 14
sequential nuclear
reactions, ultimately
stopping at lead-206.
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11.7 Ionizing Radiation
► A large dose of ionizing radiation can destroy living cells,
causing death.
► A small dose of ionizing radiation may not cause visible
symptoms but might lead to a genetic mutation or cancer.
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► Health professionals who work with X rays or other
kinds of ionizing radiation protect themselves by
surrounding the source with a thick layer of lead or
other dense material.
► Protection is also afforded by controlling the
distance between the worker and the radiation source
because radiation intensity (I) decreases with the
square of the distance from the source.
► The intensities (I) of radiation at two different
distances (d) are given by the equation:
I1d12 = I2d22
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11.8 Detecting Radiation
►We cannot see, hear, smell, touch, or taste radiation, no
matter how high the dose. We can, however, detect
radiation by taking advantage of its ionizing properties.
►The simplest device for
detecting exposure to
radiation is the
photographic film badge.
►The film is protected from
exposure to light, but any
other radiation striking the
badge causes the film to
fog.
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►The Geiger counter is
an argon-filled tube.
The inner walls are
given a negative charge,
and a wire in the center
is given a positive
charge.
►Radiation ionizes the
argon atoms, which
briefly conduct a current
between the walls and
the center electrode.
►The current is detected,
amplified, and used to
produce a clicking
sound or to register on a
meter.
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► The most versatile method for
measuring radiation in the
laboratory is the scintillation
counter.
► In this device, a substance
called a phosphor emits a
flash of light when struck by
radiation.
► The number of flashes are
counted electronically and
converted into an electrical
signal.
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11.9 Measuring Radiation
Some radiation intensity units measure the number of
nuclear decay events; others measure exposure to
radiation or the biological consequences of radiation.
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► The biological consequences of different radiation
doses are shown below.
► The average annual radiation dose is only about 0.27
rem. About 80% of this background radiation comes
from natural sources; the remaining 20% comes from
medical procedures and from consumer products.
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11.10 Artificial Transmutation
► Very few of the approximately 3300 known
radioisotopes occur naturally. Most are made from
stable isotopes by artificial transmutation, the
change of one atom into another brought about by
nuclear bombardment reactions.
► Carbon-14 is created in the upper atmosphere.
14N + 1n  14C + 1H
► Plutonium-239 is made in breeder reactors.
238U + 1n  239U  239Np + b-  239Pu + bPrentice Hall © 2007
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11.11 Nuclear Fission and Nuclear
Fusion
► Nuclear fission: The fragmenting of heavy nuclei.
► Chain reaction: A reaction that is self-sustaining.
► Critical mass: The minimum amount of radioactive
material needed to sustain a nuclear chain reaction.
► The fission of 235U produces vast amounts of heat
that can be used to produce electric power.
► Lithuania and France generate about 86% and 77%,
respectively, of their electricity in nuclear plants.
About 22% of U.S. electricity is nuclear-generated.
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Each fission event produces additional neutrons that
induce more fissions. Such chain reactions usually lead to
the formation of many different fission products.
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► Nuclear fusion: The joining together of light nuclei.
► Light nuclei such as the isotopes of hydrogen release
enormous amounts of energy when they undergo
fusion. It is fusion reactions of hydrogen nuclei to
produce helium that powers our sun and other stars.
► The necessary conditions for nuclear fusion are not
easily created on Earth.
► In stars the temperature is on the order of 2 x 107 K
and pressures approach 1 x 105 atmospheres. At
these extremes, nuclei are stripped of all their
electrons and have enough kinetic energy that
nuclear fusion readily occurs.
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Chapter Summary
► A nuclear reaction changes an atomic nucleus,
causing the change of one element into another.
► A nuclear reaction is balanced when the sum of the
nucleons is the same on both sides of the reaction
arrow and when the sum of the charges on the nuclei
plus any ejected subatomic particles is the same.
► Radioactivity is the spontaneous emission of
radiation from the nucleus of an unstable atom. a
radiation consists of helium nuclei, b radiation
consists of electrons, and g radiation consists of
high-energy light waves.
► One half-life is the amount of time necessary for
one-half of the radioactive sample to decay.
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Chapter Summary Cont.
► High-energy radiation of all types is called ionizing
radiation. When ionizing radiation strikes an atom, it
makes a reactive ion that can be lethal to living cells.
► g rays and X rays are the most penetrating and most
harmful types of external radiation; a and b particles
are the most dangerous types of internal radiation.
► The curie (Ci) measures disintegrations per second;
the roentgen (R) measures the ionizing ability; the
rad measures the amount of radiation energy
absorbed per gram of tissue; and the rem measures
the amount of tissue damage caused by radiation.
► Radiation effects become noticeable with a human
exposure of 25 rem and become lethal at an exposure
above 600 rem.
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Chapter Summary Cont.
►Transmutation is the change of one element into
another brought about by a nuclear reaction. Most
known radioisotopes do not occur naturally but are
made by bombardment of an atom with a high-energy
particle.
►In fission, the nucleus is split apart to give smaller
fragments. A large amount of energy is released
during fission, leading to its use for generating
electric power.
►Nuclear fusion results when small nuclei such as
those of tritium and deuterium combine to give a
heavier nucleus.
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End of Chapter 11
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