Nuclear Chemistry
Radioactivity
Radioisotopes are unstable isotopes whose nuclei
gain stability by spontaneously undergoing changes.
These changes are accompanied by the emission of
large amounts of energy.
Radioactive decay is the process by which materials
give off this energy.
The penetrating rays and particles that are emitted
during these changes are called radiation.
Eventually unstable radioactive isotopes are
transformed into stable isotopes of a different
element.
Radioactive Isotopes
All elements consist of at least one
radioactive isotope.
Isotopes that have too many or too few
neutrons (atomic mass larger or smaller
than the average) tend to be radioactive.
All isotopes with an atomic number greater
than 83 are radioactive.
Identify the radioactive isotope
0%
1.
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2.
0%
3.
0%
4.
1
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3
21
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1H
1
14C
6
16O
8
14N
7
4
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10
7
8
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Identify the radioactive isotope
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1. Chlorine-35
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2. Carbon-12
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3. Lead-207
0%
4. Potassium-40
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Types of Radiation
Alpha radiation
Beta radiation
Gamma radiation
Alpha Radiation
Alpha radiation consists of helium nuclei that are
emitted from a radioactive isotope.
Alpha particles consist of two protons and two
neutrons.
Alpha particles have a 2+ charge.
The symbol for an alpha particle is 42He or α.
Alpha particles are the most massive of the
radioactive particles (4 amu), the most damaging,
and are the least penetrating (easily stopped by a
piece of paper).
http://phet.colorado.edu/en/simulation/alpha-decay
http://www.hpwt.de/Kern2e.htm
What is the product when plutonium238 undergoes alpha decay?
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1. Uranium-234
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2. Thallium-206
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3. Lead-206
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4. Radium-226
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3
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What is the product when
bismuth-210 undergoes alpha decay?
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1. Radium-226
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2. Lead-206
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3. Thallium-206
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4. Uranium-232
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What is the product when polonium210 undergoes alpha decay?
0%
1. Bismuth-206
0%
2. Lead-206
0%
3. Radium-206
0%
4. Thorium-206
1
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Beta Particles
Beta particles consist of fast moving electrons
formed by the decomposition of a neutron in an
atom.
The neutron decomposes into a proton and an
electron-the proton remains in the nucleus and
the electron is emitted.
Beta particles have a 1- charge.
The symbol for a beta particle is o-1e or β.
Beta particles are 8000 x lighter than an alpha
particle, are less damaging, but are more
penetrating (stopped by aluminum foil or thin
pieces of wood).
http://phet.colorado.edu/en/simulation/betadecay
What is the product when carbon14 undergoes beta decay?
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1. Carbon-13
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2. Nitrogen-14
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3. Oxygen-14
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4. Boron-10
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What is the product when strontium-90
undergoes beta decay?
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1. Rubidium-90
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2. Krypton-91
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3. Strontium-91
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4. Yttrium-90
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What is the product when potassium-40
undergoes beta decay?
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1. Calcium-40
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2. Scandium-40
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3. Argon-40
0%
4. Chlorine 40
1
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Gamma Radiation
Gamma radiation is high energy electromagnetic
radiation.
Gamma rays are emitted along with alpha or
beta particles.
Gamma rays have no mass or charge.
The symbol for gamma rays is ooγ
Gamma rays are extremely penetrating and
potentially dangerous (stopped only by several
meters of concrete or several centimeters of
lead).
Nuclear Decay Puzzle
Uranium-238 is a radioactive isotope.
Through a series of 14 nuclear reactions,
the unstable uranium isotope undergoes
radioactive decay until it forms a more
stable isotope of lead-206.
Unstable isotopes formed during
the process:
Uranium-234
Thorium-234
Thorium-230
Protactinium-234
Radium-226
Radon-222
Polonium-218
Polonium-214
Polonium-210
Lead-214
Lead-210
Bismuth-214
Bismuth-210
Radiation emitted during the
process:
Eight alpha particles
Six beta particles
Procedure
Write the isotope symbol for each of the
radioactive isotopes involved in the problem.
Put one symbol on each card. (There should be
15 total)
On eight cards, write the symbol for alpha
radiation.
On six cards, write the symbol for beta radiation.
Put the cards in the correct order to determine
the steps in going from uranium-238 to lead-206.
After they are in the correct order, write the 14
nuclear equations that illustrate the steps.
Radioactivity and Half-Lives
Purpose: To simulate
the conversion of a
radioactive isotope
over a period of time.
Data:
Trial #
Number
of atoms
decayed
Number of
atoms
remaining
0
0
100
Analysis
Use graph paper and plot the “number of
isotopes remaining” (y-axis) vs. the trial number
(x-axis).
Examine your graph. Is the number of isotopes
remaining over time linear or nonlinear? Is the
rate constant over time or does it change?
By approximately how much did the number of
isotopes remaining decrease with each trial?
Define half-life. What represented one half-life
during this lab?
Answer the “You’re the Chemist” questions on
page 852 in your textbook.
Half-Life
A half-life is the time it takes for one -half
of the nuclei of a sample of radioactive
isotopes to undergo radioactive decay.
Half-lives may be as short as a fraction of
a second or as long as billions of years.
Half-lives of selected isotopes
Isotope
Half-life
Hydrogen-3
12.3 years
Carbon-14
5730 years
Iodine-131
8.07 days
Lead-212
10.6 hours
Polonium-194
0.7 seconds
Polonium-210
138 days
Uranium-235
710 million years
Uranium-238
4.5 billion years
Plutonium-236
2.85 years
Graph the following data
Time elapsed (days)
0
Amount of sample
remaining
100 g
5
74 g
10
50 g
15
35 g
20
25 g
25
18 g
30
12.5 g
Use the graph to answer the
following questions:
1. How much remains after 3 days?
2. What is the half-life of this isotope?
3. If 25 g remains, how much time has
elapsed?
4. How many half lives have occurred when
25 g remains?
The half-life of carbon-14 is 5700 years. If a 10
gram sample undergoes decay for 17,100 years,
how many half-lives has the sample undergone?
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1. 10
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2. 5
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3. 3
0%
4. 1
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3
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10
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How much of the sample from the previous
problems remains after 17,100 years?
10
0%
1. 10 g
0%
2. 5 g
0%
3. 2.5 g
0%
4. 1.25 g
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Cobalt-60 is a radioactive element used as a source of
radiation in the treatment of cancer. Cobalt-60 has a halflife of five years. If a hospital starts with a 1000-mg supply,
how much will remain after 10 years?
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1. 1000 mg
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2. 750 mg
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3. 500 mg
0%
4. 250 mg
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If 62.5 g of the original sample of cobalt-60
remains, how much time has elapsed?
10
0%
1. 15 years
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2. 20 years
0%
3. 25 years
0%
4. 30 years
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Determining Half-Lives
In order to solve problems involving half-lives,
the following equation may be used:
# of half-lives = total time/time of one half-live
To determine the amount of sample left, the following
equation may be used:
amount left = starting amount/ 2# of half-lives
Solve Practice Problems on page 849.
Fission
Fission-when a large nucleus is bombarded with
neutrons, a division of the nucleus into 2 smaller
nuclei occurs resulting in a large release of
energy.
Example:
• This energy is used in nuclear power
plants and in atomic bombs.
Fusion
Fusion-nuclei with small masses combine
to form a nucleus with a larger mass.
Uses of Fusion
This type of reaction occurs in the sun and
in hydrogen bombs.
The high temperature needed to start a
fusion reaction is produced by a fission
reaction.
More energy is released per gram of
reactant in fusion than in fission.
Other Uses of Nuclear
Reactions
Dating of fossils (Carbon-14)
Dating of geological time (Potassium-40)
Industrial Uses (Radiation used to monitor
and control the thickness of aluminum foil
and plastic wrap)
Nuclear imaging (MRI)
Food preservation
Medical applications