Name
CHAPTER 4
Class
Date
Atomic Energy
2 Energy from the Nucleus
SECTION
National Science
Education Standards
BEFORE YOU READ
After you read this section, you should be able to answer
these questions:
PS 3a, 3e
• What is nuclear fission?
• What is nuclear fusion?
• What are the advantages and disadvantages of
nuclear fission and nuclear fusion?
How Are Atoms Broken Apart?
Changes to atomic nuclei can release tremendous
amounts of energy. This energy can be useful but there
are risks that come with the energy. Understanding the
advantages and the disadvantages of nuclear energy helps
people make good decisions about its use.
The nuclei of some atoms decay by breaking apart.
They then form two smaller nuclei that are more stable.
During nuclear fission, a large nucleus splits into two
smaller nuclei, releasing energy at the same time.
Some large atoms, including some isotopes of uranium, break apart naturally by nuclear fission. These
kinds of large atoms can also be forced to undergo fission. This is done by hitting the nucleus of an atom with a
neutron, as shown in the figure below.
STUDY TIP
Describe Make a list of the
advantages and disadvantages
of using each type of nuclear
energy.
READING CHECK
1. Describe What happens
during nuclear fission?
Fission of a Uranium-235 Nucleus
Neutron
Uranium-235
Charge: 0
Barium-142
Energy
Neutron
Charge: 0
Charge: 56
Neutron
Krypton-90
Neutron
Charge: 0
Math Focus
2. Determine What is the
difference in mass between
uranium-235 and the sum
of the masses of barium-142
and krypton-90? Why are
they different?
Charge: 0
Charge: 92
Charge: 36
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Atomic Energy
Name
SECTION 2
Class
Date
Energy from the Nucleus continued
STANDARDS CHECK
PS 3a Energy is a property of
many substances and is associated with heat, light, electricity,
mechanical motion, sound,
nuclei, and the nature of a
chemical. Energy is transferred
in many ways.
3. Describe What happens
during nuclear fission that
gives off energy?
ENERGY FROM MATTER
The process of nuclear fission releases a lot of energy.
Where does it come from? If you could carefully measure
the mass of all the particles before and after fission, you
would find an interesting change. The total mass of the
products is slightly less than the total mass of the original nucleus and the neutron. The masses are different
because some of the mass was changed into energy.
The amount of energy given off by a single uranium
nucleus is very small. There are a large number of uranium atoms in a small sample, though. The fission of the
uranium nuclei in a pellet that is smaller than a penny
can release as much energy as burning 1,000 kg of coal.
NUCLEAR CHAIN REACTIONS
READING CHECK
4. Describe What is a
nuclear chain reaction?
What happens to the three neutrons shown as products
of the fission of uranium-235? If they each hit another
uranium-235 nucleus and those nuclei split, the fission would
produce nine more neutrons. If the neutrons continue to
cause fission, the result is a nuclear chain reaction.
In a nuclear chain reaction, a continuous series of
nuclear fission reactions occurs. A model of the beginning
of a nuclear chain reaction is shown in the figure below.
An Uncontrolled Nuclear Chain Reaction
Barium
Neutron
Energy
Uranium
Krypton
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Atomic Energy
Name
Class
SECTION 2
Date
Energy from the Nucleus continued
ENERGY FROM A CHAIN REACTION
In an uncontrolled chain reaction, huge amounts of
energy are released very quickly. An exploding atomic
bomb is an example. Keeping some of the neutrons from
hitting uranium nuclei can control the nuclear chain reaction. Then energy is released but not fast enough to cause
an explosion.
Nuclear power plants use controlled chain reactions.
They change the energy from the fission of uranium fuel
into electrical energy. The figure below shows how a
nuclear power plant works. Control rods are made of
materials that absorb neutrons without releasing energy.
In a power plant, the energy from fission is absorbed
as heat. The heat turns water into steam. Then a turbine
changes the kinetic energy of the moving water atoms
in steam into mechanical energy. A generator converts
mechanical energy into electrical energy.
Uranium-235
nuclei in the
fuel rod (black)
undergo a
chain reaction.
Control rods
(gray) absorb
neutrons. This
keeps the
chain reaction
at a safe level.
2
5. Describe How is a nuclear
chain reaction controlled?
READING CHECK
6. Identify What are two
energy changes that take
place after heat is changed to
steam in a power plant?
How a Nuclear Power Plant Works
1
READING CHECK
A coolant, usually
water, absorbs energy
from the chain reaction.
3
Water absorbs
energy from the hot
coolant and changes
to steam.
To cooling
tower
4
5
The steam
turns a turbine
attached to a
generator.
The generator changes the mechanical
energy of the spinning turbine into
electrical energy.
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Atomic Energy
Name
SECTION 2
Class
Date
Energy from the Nucleus continued
How Is Fission Harmful or Helpful?
Every kind of energy has advantages and disadvantages. To make decisions about using nuclear power,
people need to know both.
ACCIDENTS
READING CHECK
One of the concerns about nuclear power is shown in
the figure below. In 1986 an accident occurred at a nuclear
power plant at Chernobyl, Ukraine. An explosion blew a
large amount of radioactive fuel and waste into the atmosphere. The cloud spread over much of Europe and Asia,
and some material even reached North America.
7. Describe What can happen
during a nuclear accident?
During a test at the
Chernobyl nuclear
power plant, the
emergency protection
system was turned off.
The reactor overheated,
causing an explosion.
RADIOACTIVE WASTE
READING CHECK
8. Describe Why must some
radioactive waste be stored
for thousands of years?
READING CHECK
9. Identify What gas,
produced by burning fossil
fuels, is not released into the
atmosphere by nuclear power
plants?
Another reason people are concerned about nuclear
power is radioactive waste. The waste includes used fuel
rods, chemicals used to process uranium, and even the
workers’ protective clothing. Some of this waste will have
dangerous levels of radioactivity for thousands of years.
That means it must be stored for a very long time before
it is safe.
NUCLEAR VERSUS FOSSIL FUELS
Even though there are concerns about nuclear power,
there are also advantages. Nuclear power plants use a lot
less fuel than plants that burn fossil fuels. They can be
much less expensive to operate.
Nuclear power plants do not release gases, such as
carbon dioxide given off by burning fossil fuels, into the
atmosphere. That means they do not contribute to climate
change and other pollution problems. Using nuclear power
allows the supply of fossil fuels to last longer. However,
the supply of uranium fuel is also limited.
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Atomic Energy
Name
SECTION 2
Class
Date
Energy from the Nucleus continued
How Are Atoms Put Together?
Fusion is another nuclear reaction in which matter
is converted to energy. In nuclear fusion, two or more
nuclei that have small masses combine to form a larger
nucleus.
Two positively charged nuclei repel one another. In
order for fusion to occur, they must be forced very close
together. Fusion requires very high temperatures—more than
100,000,000°C! At this temperature, the electrons are removed
from atoms, forming a state of matter called plasma.
In plasma, the positive nuclei and electrons are separated. This happens in the core of the sun and other stars.
Hydrogen nuclei in stars fuse to form helium nuclei as
shown in the figure below.
Nuclear Fusion of Hydrogen
Beta particle
(positron)
Helium-4
Hydrogen-1
Hydrogen-1
Charge: 1
READING CHECK
10. Describe What happens
during nuclear fusion?
READING CHECK
11. Identify Where, in the
sun, is plasma found?
Charge: 1
Charge: 1
Energy
Hydrogen-1
Hydrogen-1
Charge: 1
Beta particle
(positron)
Charge: 1
Charge: 1
Charge: 2
ADVANTAGES AND DISADVANTAGES OF FUSION
Nuclear fusion is not used yet to make energy electricity for your home. Scientists cannot yet control the high
temperatures well enough use fusion. Also, it takes more
energy to hold the plasma together than we can get from
the fusion. Fusion power plants may exist once these
problems are solved.
If a fusion power plant were to have an accident, it
would not release large amounts of radioactive material.
The process does not release any pollutants, so fusion
energy would be a clean energy source.
Another advantage is that there is enough fuel in
Earth’s water to provide energy for millions of years.
Many scientists think that producing energy from fusion
will be possible in the future. However, this will require a
large amount of money to pay for research.
READING CHECK
12. Describe Why can’t we
use nuclear fusion to make
electricity for homes today?
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Atomic Energy
Name
Class
Section 2 Review
Date
NSES
PS 3a, 3e
SECTION VOCABULARY
nuclear chain reaction a continuous series of
nuclear fission reactions
nuclear fission the process by which the
nucleus of a heavy atom splits into two or
more fragments; the process releases neutrons
and energy
nuclear fusion the process by which nuclei of
small atoms combine to form a new, more
massive nucleus; the process releases energy
1. Describe Where do the neutrons for nuclear fission come from in a nuclear chain
reaction? What do they do after they are set free by fission?
2. Make inferences What could happen in a nuclear fission power plant if the
control rods could not be put into place?
3. Analyze Processes In a nuclear power plant, the energy is converted into
different forms several times. Describe two of these changes and explain why
they are necessary.
4. Make Judgments In terms of radioactive wastes, why would fusion be a better
source for making electricity than a fission power plant?
5. Determine During the nuclear fission of plutonium-244, barium-144 is produced,
along with an unknown nucleus and three neutrons. What must be the mass of
the unknown nucleus? Show your work.
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Atomic Energy
L
Interactions of Matter Answer Key continued
12. the information that the cell needs to build
14. Dark area should be circled.
15. Check for leaks in pipes and flaws in metal
protein molecules
Review
1. Type of carbon
backbone
objects.
16. carbon-14
17. one half-life, two half-lives
18. A little less than half of the carbon-14 had
decayed after his death.
Description
Ring
The chain of carbon atoms forms
a ring.
Straight chain
All carbon atoms are connected in
a straight line.
Branched chain
The chain of carbon atoms
separates into different
directions.
Review
1. The atomic number for both isotopes is 92.
The mass number of uranium-235 is 235, and
the mass number of uranium-238 is 238.
2. First column, top to bottom: alpha, beta,
gamma
Second column: particle (electron)
Third column, top to bottom: 4, 0
Fourth column, top to bottom: 1-, 0
Last column, top to bottom: low, high
3. Gamma rays would work because they have
the most penetrating power and enough
energy to pass through metal. Alpha and
beta particles would be stopped by the
metal parts.
4. One-fourth remaining indicates 2 half-lives
or 2.6 billion years.
2. saturated compounds—alkanes,
unsaturated compounds—alkenes and alkynes
3.
Type of biochemical
Description
Proteins
made of hundreds or
thousands of amino acid
molecules
Nucleic acids
one of the functions is to
store genetic information
Carbohydrates
made of one or more
simple sugar molecules
Lipids
one of the functions is to
store energy
4. DNA—contains the genetic material of a cell;
RNA—contains the information that the cell
needs to build protein molecules.
SECTION 2 ENERGY FROM THE NUCLEUS
1. A large nucleus splits into two smaller
Chapter 4 Atomic Energy
nuclei, releasing energy.
2. Their difference is three because three neu-
SECTION 1 RADIOACTIVITY
1. Energy came from the uranium.
2. radioactive decay
3. An alpha particle has two protons and two
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
3.
4.
neutrons. Mass number is the sum of the
protons and neutrons in a nuclear particle or
in a nucleus.
224
mass and charge
It stays the same.
5+
atoms that have the same number of protons
but different number of neutrons
high-energy waves
They have more mass and charge, so they
tend to interact with atoms more easily.
They penetrate matter deeply.
to warn them if they have been exposed to
radiation harmful enough to damage cells
follow the path of a process
5.
6.
7.
8.
9.
10.
11.
12.
trons are also produced.
Some of the masses are changed into energy.
a continuous series of nuclear fission
reactions
by keeping some of the neutrons from hitting a uranium nucleus
kinetic energy changed into mechanical
energy, mechanical energy changed into
electrical energy
An explosion can blow a large amount
of radioactive fuel and waste into the
atmosphere.
It has dangerous levels of radioactivity.
carbon dioxide
Two or more nuclei that have small masses
combine to form a larger nucleus.
the core
Scientists cannot yet control the high temperatures well enough to use fusion.
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Interactive Textbook Answer Key
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Interactions of Matter
L
Interactions of Matter Answer Key continued
Review
1. The neutrons come from the nucleus of
2.
3.
4.
5.
the atom that split. These neutrons continue
the chain reaction by causing other fission
reactions.
Without the control rods, an uncontrolled chain
reaction could occur in the fuel and release
energy too quickly or even cause an explosion.
Answers include: nuclear energy to heat
energy, heat energy to mechanical energy,
mechanical energy to electrical energy
The conversions are needed because we
cannot use the nuclear or heat energy
directly in homes and factories. The process
changes energy that can be used at only one
place to energy that can be delivered.
If a fusion power plant were to have an accident, it would not release large amounts of
radioactive material.
244  (144  3)  97
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Interactions of Matter