Download Radioactive Elements (pages 139–146)

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Radioactive Elements
Radioactivity
(pages 139–146)
(pages 140–141)
Key Concept: In 1896, the French scientist Henri
Becquerel discovered radioactive decay quite by
accident while studying a mineral containing uranium.
• A nuclear reaction is a reaction that involves the
nucleus of an atom. A nuclear reaction can change an
element into a different element.
• Some isotopes of elements break apart naturally.
Radioactive decay is a process in which the nuclei of
unstable isotopes give off atomic particles and energy.
• Radioactive decay was first discovered by Henri
Becquerel. He observed that uranium gives off energy
all by itself all the time.
• Radioactivity is the energy and atomic particles given
off by an unstable nucleus. Nuclear reactions cause
radioactivity.
Answer the following questions. Use your textbook and the
ideas above.
1. Draw a line from each term to its meaning.
Term
Meaning
nuclear
reaction
a. the energy and atomic particles
given off by an unstable nucleus
radioactive
decay
radioactivity
b. a reaction that involves the
nucleus of an atom
c. the process in which nuclei
give off atomic particles and
energy
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2. Is the following sentence true or false? A nuclear
reaction can change an element to another element.
Types of Radioactive Decay
(pages 141–142)
Key Concept: Natural radioactive decay can produce
alpha particles, beta particles, and gamma rays.
• Radiation is the particles and energy given off during
radioactive decay. The three forms of radiation are alpha
particles, beta particles, and gamma radiation.
• An alpha particle is made up of two protons and two
neutrons. When an atom releases an alpha particle, the
atom’s atomic number decreases by 2. The atom has
become a different element.
• A beta particle is a fast-moving electron given off by a
nucleus. A beta particle forms when an unstable neutron
changes into a proton and an electron. The proton stays
in the nucleus, and the electron is the beta particle. The
atomic number of the atom increases by 1. The atom is
a different element.
• Gamma radiation is the energy that is released in a
nuclear reaction. Whenever an alpha particle or a beta
particle is released, gamma radiation is also released.
The release of gamma radiation does not change the
atomic number of an atom.
Answer the following questions. Use your textbook and the
ideas above.
3. Circle the letter of the form of radiation that does NOT
change the atomic number of an atom.
a. alpha particle
b. beta particle
c. gamma radiation
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4. The picture shows radioactive decay in which an alpha
particle is produced.
a. Circle the alpha particle.
b. After releasing the alpha particle, how has the atom
changed?
a. The atom has not changed.
b. The atomic number of the atom has decreased
by 2.
c. The atomic number of the atom has increased
by 2.
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Using Radioactive Isotopes
(pages 142–146)
Key Concept: Uses of radioactive isotopes include
determining the ages of natural materials on Earth,
tracing the steps of chemical reactions and industrial
processes, diagnosing and treating disease, and
providing sources of energy.
• Radioactive isotopes are useful for two reasons. First,
radioactive isotopes change into different elements.
Second, radioactive isotopes give off radiation that can
be observed.
• When radioactive isotopes break down, not all of the
atoms in a sample break down at the same time. Halflife is the length of time it takes for half of the atoms in a
sample to break down. Every isotope has a different
half-life.
• Half-life is useful in finding out the age of rocks and
fossils. This process is called radioactive dating.
• Because radiation can be observed, a radioactive
isotope can be used to follow the steps of a chemical
reaction. Tracers are radioactive isotopes used to trace
the steps of a reaction. Doctors use tracers to find
medical problems and kill unhealthy cells.
• Some power plants use the energy given off by the
decay of radioactive isotopes to make electricity.
• Radioactive materials are dangerous. Radiation can kill
healthy body cells and upset the chemical reactions in
the body.
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Answer the following questions. Use your textbook and the
ideas on page 61.
5. Circle the letter of each sentence that is true about why
radioactive isotopes are useful.
a. Radioactive isotopes change into different
elements.
b. Radioactive isotopes can upset chemical reactions
in the body.
c. Radioactive isotopes give off radiation that can be
observed.
6. Draw a line from each term to its meaning.
Term
Meaning
half-life
a. radioactive isotopes used to trace
the steps of a reaction
radioactive
dating
b. using radioactive isotopes to find
out the age of rocks and fossils
tracers
c. the length of time it takes for half
of the atoms in a radioactive
sample to break down
7. How do doctors use radioactive isotopes?
a. to find the age of a person
b. to kill unhealthy cells in the body
c. to make electricity
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