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Topic 12
Nuclear
Chemistry
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Topic 12-Nuclear Chemistry
Stability of the Nuclei
a. Elements with atomic number 84 and above
b. Proton to neutron ratio
Common forms of radiation-Table O
Nuclear equations
a. Be able to balance
Fission
Fusion
Artificial vs. Natural Transmutation
Half-life
a. Be able to solve problems
Uses and Dangers of Radioisotopes
a. Dating
b. Chemical tracers
c. Industrial applications
d. Medical Applications
Radiation Risks
Nuclear Chemistry
Most chemical reactions involve either the exchange or sharing of
electrons between atoms. Nuclear chemistry is quite different in
nature because it involves changes in the nucleus.
When the atomic nucleus of one element is changed into the
nucleus of a different element, the reaction is called a transmutation
Most nuclei are stable, that is, they are found within the
“belt of stability.” It is the ratio of neutrons to protons that
determines the stability of a given nucleus.
Elements with atomic number 84 and above, have no stable
isotopes (radioisotopes).
Zone of Stability
Plot of proton to neutron ratio
showing the stable isotopes
If the proton to neutron ratio of an
atom falls outside of the zone of
stability, it is an unstable isotope
Common Forms of Radiation
Table O
Marie Curie
November 7, 1867-July 4, 1934
First woman to win a Nobel Prize, the only woman to win in two
fields and the only person to win in multiple sciences.
Because of their levels of radioactivity, her papers from the 1890s
are considered too dangerous to handle. Even her cookbook is
highly radioactive. Her papers are kept in lead-lined boxes, and
those who wish to consult them must wear protective clothing.
Mass number
charge
4He
2
Notice gamma radiation has no mass and no charge.
It is NOT a particle but instead it is a ray.
The alpha particle is a helium nucleus
The beta particle is an electron
Name
Penetrating Power
Ionizing Power
Alpha
Weak
Strong
Beta
Average
Average
Gamma
Strong
Weak
Because gamma has the greatest penetrating power, it is the
type of radiation that is most dangerous to humans.
Ionizing power is the ability of radiation to knock electrons off
some atoms of the bombarded substance to produce ions.
Anything that is radioactive may give off alpha or beta particles.
Anything radioactive will always give off gamma radiation.
Therefore, anything radioactive is dangerous to humans.
Why does the beta particle deflect to the + side of the electric field?
Beta has a – charge and is attracted to the + electric field
Why does the alpha particle deflect to the – side of the electric field?
Alpha has a + charge is attracted to the – electric field
Why does the gamma ray pass through undeflected?
Gamma has no charge and is unaffected by the field
Opposite charges attract
Alpha Decay
When an unstable nucleus emits an alpha particle, the nucleus
is called an alpha emitter.
Alpha decay can be summarized as follows:
1. Atomic number decreases by two
2. Number of protons (charge) decreases by two
3. Number of neutrons decreases by two
4. Mass number decreases by four
Mass #
(p + n)
226Ra
88
4He
 222
Rn
+
86
2
# protons (charge)
Beta Decay
A nucleus that emits a beta particle as a result of a nuclear
disintegration is said to undergo beta decay and is called a
beta emitter
Beta decay can be summarized as follows:
1. Atomic number increases by one
2. Number of protons increases by one
3. Number of neutrons decreases by one
4. Mass number remains the same
Mass #
(p + n)
214Pb
82
0e
 214
Bi
+
83
-1
# protons (charge)
One of the things you must be able to do is balance a nuclear
equation. It must be balanced in terms of mass, charge and
energy.
The mass numbers on both sides of the equation add up to 18
18
14N
7
18
+ 42He  178 O + 11H
9
9
The atomic numbers (charges) on both sides of the equation add
up to 9
Lets try some:
27Al
13
+ 1n  24Na + X
0
1.
11
2.
14C
6
 X + -10e
3.
12C
6
257Rf + 4X
+ 249
Cf

98
104
X = 4He
2
X = 14N
7
X= 01n
Fission Reactions
A fission reaction begins with the capture of a neutron by the
nucleus of a heavy element. The nucleus produced by the capture
is unstable. It immediately splits, undergoing the process of fission.
1n
0
+ 235U  142Ba + 91Kr + 301n + energy
92
56
36
The products of fission are radioactive and must be safely stored
until they become stable. This presents a huge problem since
some of these products are radioactive for thousands of years.
We harness the energy produced and use it for turning the turbines
to generate electricity or for use in nuclear weapons
Fusion Reactions
Involve the combining of light nuclei to form heavier ones
1H
1
+ 11H  12H ++10e
1H
1
+ 21H  23He
3He
2
+ 23He  24He + 211H
3He
2
+ 11H 42He ++10e
While these reactions produce the energy from the sun, they are
not yet available to produce energy here on Earth. Extremely
high temperatures and pressure are needed to allow the positively
charged hydrogen nuclei to fuse into helium.
Remember the nuclei are positively charged and repel each other
and resist being fused together
Fission and Fusion
In both types of reactions, the total mass of the products is less
than the total nuclear mass of the reactants
This loss of mass seems to contradict our concept that matter
(mass) can neither be created or destroyed. The loss of mass in
these nuclear reactions represents a conversion of some matter
into a large amount of energy.
This relationship was expressed by Albert Einstein in his
famous equation:
E = mc2
A minute amount of matter produces an extremely large amount
of energy
Particle Accelerators
Accelerate the speed/velocity of particles by using electrical
and magnetic fields.
Neutrons cannot be accelerated by particle accelerators
because they are neutral and cannot be affected by these fields
Transmutations
Nuclear reactions can be either naturally occurring or artificial.
Natural transmutation- Occur by radioactive decay
18F
9
 178 O + 11H
Notice that the element changed without us having to do anything
to it
Artificial transmutation- Occur when particles bombard the
nucleus of the atom
9Be
4
+ 42He  126 C + 10n
Notice that the element has to be bombarded with a particle
before it will change
Half-Life
Radioactive substances decay at a constant rate that is not
dependent on factors such as temperature, pressure or
concentration. It is also a random event. It is impossible to
predict when a given unstable nucleus will decay. However, the
number of unstable nuclei that will decay in a given time in a
sample of the element can be predicted.
The time it takes for half of the atoms in a given sample of an
element to decay is called the half-life of the element.
Half-Life
Table N
Table N gives you the half-life
of selected radioisotopes and also
gives you the decay mode of these
radioisotopes also
Notice that after each half-life, half of the radioactive
sample remains
Most chromium atoms are stable, but Cr-51 is an unstable
isotope with a half-life of 28 days.
a. What fraction of a sample of Cr-51 will remain after
168 days?
28
56
112
140
168
84
1/1
1/2
1/4
1/8
1/16
1/32
1/64
b. If a sample of Cr-51 has an original mass of 52 g, what
mass will remain after 168 days?
28
168
56
84
112
140
52
26
13
6.5
3.25
1.63
.813
How much was present originally in a sample of Cr-51 if 0.75 mg
remains after 168 days?
28
?
56
24.0
112
84
12.0
6.0
48 mg
140
3.0
168
1.5
.75
In 6.20 hours, a 200 g sample of Ag-112 decays to 50 g. What is
the half-life of Ag-112?
6.20 h
200
100
50
It underwent 2 half –lives (2 arrows), so we divide 6.20 by 2
6.20/2 = 3.10 hours
Half-life of Ag-112 is 3.10 hours
Uses and Dangers of Radioisotopes
Radioisotopes have many practical applications in industry,
medicine and research. They also have potential dangers
because of harm that could be done by the radiation released.
1. Dating
C-14 decays to form stable C-12 is used to date living or
once alive materials
U-238 decays to form stable Pb-206 and is used to date
geologic formations
2. Chemical Tracers
Any radioisotope used to follow the path of a material in a system
If P-31 is present in fertilizer administered to a plant, the uptake
of the radioactive phosphorus can be traced by detectors.
Scientists can then determine the proper amounts and timing of
fertilizer applications.
3. Medical Applications
Certain radioisotopes that are quickly eliminated from the body
and have short half-lives are important as tracers in medical
diagnosis
I-131-uses in both the detection and treatment of thyroid
conditions
Co-60-aimed at cancerous tumors and kills cells of tumor
Some radioisotopes are used to irradiate food and kill bacteria.
The food lasts longer without spoiling and causes fewer bacterial
Infections in those who consume it
Tc-99-absorbed by cancerous cells and is easily detected by a scan.
Radiation Risks
1. Kill cancerous cells but have the potential to damage normal cells
2. High doses of radiation can cause serious illness and death
3. Radiation can cause mutations in sex cells that could
potentially be passed from generation to generation
4. Nuclear power plants have waste products with long half-lives
which make them difficult to store and dispose of