Nuclear Changes
Section 1
Section 1: What is Radioactivity?
Preview
• Key Ideas
• Bellringer
• Nuclear Radiation
• Nuclear Decay
• Math Skills
• Radioactive Decay Rates
Nuclear Changes
Section 1
Key Ideas
〉What happens when an element undergoes
radioactive decay?
〉How does radiation affect the nucleus of an
unstable isotope?
〉How do scientists predict when an atom will
undergo radioactive decay?
Nuclear Changes
Section 1
Bellringer
Before studying about nuclear chemistry, answer the
following items to refresh your memory about the structure
of the nucleus.
1. Label the diagram below.
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Bellringer, continued
2. Complete the table below to indicate how many protons and
neutrons are in the nuclei of each atom.
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SPS3.a&b Differentiate
between alpha and beta
particles and gamma
radiation and between
fission and fusion.
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EQ: What are the
components of
radioactivity and what
are the types of nuclear
reactions?
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Nuclear Radiation
What happens when an
element undergoes
radioactive decay?
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10-1-1 Nuclear Radiation
After radioactive decay,
the element changes into
a different isotope of the
same element or into an
entirely different element.
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10-1-2 Nuclear Radiation
• radioactive decay: the
disintegration of an
unstable atomic nucleus
into one or more different
nuclides
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10-1-3 Nuclear Radiation,
continued
• nuclear radiation: the
particles that are
released from the
nucleus during
radioactive decay
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10-1-4 Nuclear Radiation,
continued
nuclear radiation can contain
•alpha particles
•beta particles
•gamma rays
•neutrons
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10-1-5 Types of Nuclear
Radiation
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10-1-6 Nuclear Radiation,
continued
• alpha particle: a positively
charged particle that consists
of two protons and two
neutrons and that is emitted
from the nucleus during
radioactive decay
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10-1-7 Nuclear Radiation,
continued
•beta particle: an
electron or positron that
is emitted from a
neutron in a nucleus
during radioactive
decay
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10-1-8 Nuclear Radiation,
continued
•Gamma rays are highenergy electromagnetic
radiation.
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10-1-9 Nuclear Radiation,
continued
•gamma ray: a highenergy photon emitted
by a nucleus during
fission and radioactive
decay
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10-1-10 Nuclear Radiation,
continued
•Neutron emission
consists of matter that
is emitted from an
unstable nucleus.
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10-1-11 Nuclear Radiation,
continued
•Neutrons are able to
travel farther through
matter than either alpha
or beta particles.
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Nuclear Decay
How does radiation affect
the nucleus of an
unstable isotope?
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10-1-12 Nuclear Decay
Anytime that an unstable
nucleus emits alpha or
beta particles, the
number of protons or
neutrons changes.
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10-1-13 Nuclear Decay
• Nuclear-decay equations
are similar to those used
for chemical reactions.
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10-1-14 Nuclear Decay, continued
• Gamma decay changes
the energy of the nucleus,
but not the atomic number
or the atomic mass of the
element.
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10-1-15 Nuclear Decay, continued
• The atomic number
changes during beta
decay, but not the mass
number.
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10-1-16 Nuclear Decay, continued
In beta decay the atomic
number of the product
nucleus increases by 1
and the atom changes to
a different element.
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10-1-17 Nuclear Decay, continued
• A beta decay process occurs
when carbon-14 decays to
nitrogen-14 by emitting a
beta particle.
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10-1-18 Nuclear Decay, continued
• Both atomic mass and number
change in alpha decay.
–The atomic mass decrease by 4.
–The atomic number decreases
by 2.
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Visual Concept: Alpha, Beta, and
Gamma Radiation
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Math Skills
Nuclear Decay
Actinium-217 decays by releasing an alpha particle. Write
the equation for this decay process, and determine which
element is formed.
1. Write down the equation with the original element on
the left side and the products on the right side.
217
89
Ac  X  He
A
Z
4
2
X = unknown product; A = unknown mass;
Z = unknown atomic number
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Math Skills, continued
2. Write math equations for the atomic and mass numbers.
217 = A + 4
89 = Z + 2
3. Rearrange the equations.
A = 217 – 4
Z = 89 – 2
A = 213
Z = 87
4. Rewrite the equation with all nuclei represented.
The unknown decay product has an atomic number of
87, which is francium.
217
89
Ac 
213
87
Fr  42 He
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Radioactive Decay Rates
How do scientists predict
when an atom will
undergo radioactive
decay?
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10-1-19 Radioactive Decay Rates
• half-life: the time required
for half of a sample of a
radioactive isotope to break
down by radioactive decay
to form a daughter isotope
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10-1-20 Radioactive Decay
Rates, continued
Scientists can also use
half-life to predict how
old an object is.
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Math Skills
Half-Life
Radium-226 has a half-life of 1,599 years. How long will
seven-eighths of a sample of radium-226 take to decay?
1. List the given and unknown values.
Given:
half-life = 1,599 years
fraction of sample decayed = 7/8
Unknown: fraction of sample remaining = ?
total time of decay = ?
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Math Skills, continued
2. Calculate the fraction of radioactive sample remaining.
fraction of sample remaining = 1 – fraction decayed
7 1
fraction of sample remaining = 1  
8 8
3. Determine how much of the sample is remaining after each half-life.
1
amount of sample remaining after one half-life =
2
1 1 1
 
2 2 4
1 1 1 1
amount of sample remaining after three half-lives =   
2 2 2 8
amount of sample remaining after two half-lives =
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Math Skills, continued
4. Multiply the number of half-lives by the time for each half-life to
calculate the total time required for the radioactive decay.
Each half-life lasts 1,599 years.
total decay time = 3 half-lives 
1,599 y
 4,797 y
half-life
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Radioactive Decay Rates, continued
• Radioactive decay is exponential decay.
• decay curve: a graph of the number of radioactive parent
nuclei remaining in a sample as a function of time
• Carbon-14 is used to date materials.
– The ratio of carbon-14 to carbon-12 decreases with
time in a nonliving organism.
– By measuring this ratio and comparing it with the ratio
in a living plant or animal, scientists can estimate how
long ago the once-living organism died.
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Section 1
Radioactive Decay of Carbon-14