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NUCLEAR CHEMISTRY
Text Book Chapter 25
OBJECTIVES
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Stability of isotopes is based on the ratio of neutrons and protons in its nucleus. Although most
nuclei are stable, some are unstable and spontaneously decay, emitting radiation. (3.1o)
Each radioactive isotope has a specific mode and rate of decay (half-life). (4.4a)
A change in the nucleus of an atom that converts it from one element to another is called
transmutation. This can occur naturally or can be induced by the bombardment of the nucleus
by high-energy particles. (5.3a)
Spontaneous decay can involve the release of alpha particles, beta particles, positrons and/or
gamma radiation from the nucleus of an unstable isotope. These emissions differ in mass,
charge, and ionizing power, and penetrating power. (3.1p)
Nuclear reactions include natural and artificial transmutation, fission, and fusion. (4.4b)
There are benefits and risks associated with fission and fusion reactions. (4.4f)
Nuclear reactions can be represented by equations that include symbols which represent atomic
nuclei (with the mass number and atomic number), subatomic particles (with mass number and
charge), and/or emissions such as gamma radiation. (4.4c).
Energy released in a nuclear reaction (fission or fusion) comes from the fractional amount of
mass converted into energy. Nuclear changes convert matter into energy. (5.3b)
Energy released during nuclear reactions is much greater than the energy released during
chemical reactions. (5.3c)
There are inherent risks associated with radioactivity and the use of radioactive isotopes. Risks
can include biological exposure, long-term storage and disposal, and nuclear accidents. (4.4e)
Radioactive isotopes have many beneficial uses. Radioactive isotopes are used in medicine and
industrial chemistry, e.g., radioactive dating, tracing chemical and biological processes, industrial
measurement, nuclear power, and detection and treatment of disease. (4.4d)
DISCOVERY OF RADIOACTIVITY
____________________ was familiar with Wilhelm Conrad Roentgen’s accidental
discovery of mysterious rays in 1895 and chose to study related phenomenon.
In March 1896, due to some bad weather, Becquerel was unable to use the sun
for his external energy source for his experiments. He put his photographic plates
away in a drawer which also happened to contain some uranium containing
crystals. The plates were exposed, suggesting that the crystals emitted rays on
their own!
_____________________________ discovered Polonium and introduced the term
“radioactive”. Marie Curie suggested that radiation is an atomic property of
matter – not an independent emanation.
In 1899 _________________________ discovered that uranium compounds
produce three different kinds of radiation. He separated the radiation according
to their penetrating abilities and named them α (alpha), β (beta) and γ (gamma)
after the first three letters in the Greek alphabet.
STABILITY OF NUCLEI
Nuclei are composed of combinations of ______________ and _______________.
The ratio of these nucleons
determines the stability of any given
nucleus. Most nuclei are stable, but
some are unstable. Stable isotopes
have between a 1:1 and 1.5:1 ratio of
protons and neutrons. Most unstable
isotopes have twice as many
neutrons as protons.
Unstable nuclei will spontaneously decay, emitting ______________________.
All elements with an atomic number higher than 83 are radioactive.
TYPES OF DECAY
See Table O for Symbols Used in Nuclear Chemistry
ALPHA DECAY
An alpha particle is a ___________ nucleus, with2 protons and 2 neutrons.
It is represented by the symbol __________ or __________.
Alpha radiation can be stopped by a piece of paper. It has ___ penetrating power.
Because the alpha particle contains 2 protons, when an atom releases an alpha particle, its atomic
number would decrease by __________. This means it is a new element!!!!
Consider radium-226:
Before the decay
After alpha decay
Number of protons
Number of neutrons
Total mass
Number of protons
Number of neutrons
Total mass
What happened to the atomic number? _________________
What happened to the mass number? _________________
Writing this as an equation, to the left of the arrow we write the symbol for the atom before the
decay. To the right of the arrow we write the symbol for the atom that remain AND the radiation that
was emitted.
Ra 
BETA DECAY
A beta particle is equivalent to an _________ (as a neutron converts to a proton).
n  p +e
It is represented by the symbol _________ and has a charge of __________.
It has a ______________ penetrating power, needing ~6mm of aluminum to stop most beta particles.
Consider lead-214:
Before the decay
After beta decay
Number of protons
Number of neutrons
Total mass
Number of protons
Number of neutrons
Total mass
What happened to the atomic number? _________________
What happened to the mass number? _________________
Write the equation:
Pb 
GAMMA DECAY
A gamma ray is a wave of energy, (not a particle) resulting from an energy change within the
nucleus. It has no mass or charge. Gamma radiation doesn’t change the state of the nucleus, it
just carries some energy away. Gamma rays are emitted along with alpha or beta particles.
Gamma rays have ________ penetrating power. It takes a thick sheet of metal, such as lead, or
concrete to reduce them significantly.
POSITRON EMISSION
A positron is emitted during the conversion of a proton to a neutron. p  n + e
It is represented by the symbol _________ and has a charge of __________.
Consider potassium-37:
Before the decay
After positron decay
Number of protons
Number of neutrons
Total mass
Number of protons
Number of neutrons
Total mass
What happened to the atomic number? _________________
What happened to the mass number? _________________
Write the equation:
Particle
Alpha
Beta
Positron
Gamma
K 
Mass
Charge
4 amu
+2
0 amu
-1
0 amu
+1
0 amu
None
Symbol
Penetrating Power
Low
Moderate
Moderate
High
NUCLEAR EQUATIONS
Nuclear reactions can be represented by equations that include symbols which represent
atomic nuclei (with mass number and atomic number), subatomic particles (with mass and
charge) and emitted particles.
REMEMBER:
 The masses on both sides of the equation must be equal
 The charges on both sides of the equation must be equal
222
1.
86
4
Rn ---------> ________ +
234
2.
______
--------->
3.
Th --------->
90
4
90Th
230
+
88Ra
+ ______
5.
0
Pb ---------> ______+
82
234
92
U --------->
2He
226
214
4.
2He
-1e
234
93Np
+ _______
Determine the type of emission given off by each element by looking at TABLE N.
Try writing equations for the following emissions:
235U

232Th
60Co


Iron-53
TRANSMUTATIONS
A change in the nucleus of an atom changes it to a new type of atom (i.e. a new element). This
is called ______________________. Transmutation can occur naturally or artificially.
Spontaneous decay can involve the release of different particles from the nucleus.
___________________ transmutation requires the bombardment of a nucleus by high energy
particles.
FISSION
Nuclear fission occurs when the heavy nucleus of an atom is split into two lighter nuclei,
releasing neutrons and energy. This can be initiated artificially by "shooting" the nucleus with
a neutron. The lighter elements that form are more stable.
U + n  Ba + Kr + n + Energy
Since neutrons are released, they can be captured by other uranium atoms causing them to
split. This results in a _______________________, which can be controlled (as in the case of a
nuclear reactor) or uncontrolled (atomic bomb).
NUCLEAR POWER PLANT
Boiling Water
Reactor (BWR)
The boiling
water reactor
operates in
essentially the
same way as a
fossil fuel
generating
plant. In the
BWR fission
produces he
heat that boils
water in the
reactor core.
Steam from the
boiling water powers a turbine that drives a generator to produce electricity. The reactors at northeastern
Japan’s Fukushima Naiishi plant damaged in the March 2011 earthquake and tsunami are BWRs.
Pressurized Water Reactor (PWR) In the PWR plant, a pressurizer unit keeps the water that is flowing through
the reactor vessel under very high pressure to prevent it from boiling. The hot water then flows into the steam
generator where it is converted to steam. The steam passes through the turbine which produces electricity.
About two-thirds of the reactor power plants in the U.S. are of the PWR type.
FUSION
Nuclear fusion combines two light nuclei to form heavier nuclei. Nuclear fusion is the process
that powers the sun.
The mass of the new nucleus formed by fusion is less than the sum of the two reactants. The
difference in mass was converted to energy. E = mc2
To do this, nuclear fusion requires very high temperatures, and is not yet ready for practical
use.
Deuterium-tritium reaction
H + H  He + n + Energy
HALF-LIFE
Each isotope has a specific mode and rate of decay. (see Table N)
The rate of decay is called __________________. It is the time required for half of
the atoms in any given quantity of a radioactive isotope to decay. Half-life is a
____________________ that can never be changed.
For example, the half life of U-238 is __________________. That means, in 4.5
billion years half of the uranium-238 on earth will have decayed into other
elements. In another 4.5 billion years, half of the remaining uranium-238 will have
decayed. One fourth of the original material will remain after 9 billion years.
X grams ---------- X/2 grams ---------- X/4 grams ----------- X/8 grams
1half life
2nd half life
3rd half life
½ of sample still radioactive after 1 half life
¼ of sample still radioactive after 2 half lives
1/8 of sample still radioactive after 3 half lives
# OF HALFLIVES
AMOUNT
REMAINING
TIME ELAPSED
MASS OF SAMPLE
USES AND DANGERS OF RADIOISOTOPES
USES
Radioactive isotopes may be used in:
RISKS
The risks associated with using radioactive isotopes include:
VOCABULARY
Alpha particle
Artificial transmutation
Atomic number
Beta particle
Chain reaction
Decay
Emit
Fission
Fusion
Gamma ray
Half-life
Isotope
Mass number
Natural transmutation
Nucleon
Positron
Radioisotope
Tracer
Transmutation
NAME: _______________________________________
NUCLEAR
BIG IDEAS
UNSTABLE NUCLEUS
NATURAL DECAY
Particle
Alpha
Beta
Positron
Gamma
Mass
Charge
Symbol
Penetrating Power
EQUATIONS
Conservation of mass & charge
ARTIFICIAL DECAY
FISSION
Controlled
Uncontrolled
FUSION
HALF LIFE
# OF
HALFLIVES
AMOUNT
REMAINING
USES & RISKS
REFERENCE TABLES
Table O
Table N
TIME
ELAPSED
MASS OF
SAMPLE