Nuclear Chemistry
Objectives:
1.
Understand the different types of radioactivity.
2.
Identify radioactive elements and be able to predict the mode of decay.
3.
Be able to write balanced nuclear reactions.
4.
5.
7.
Understand what is meant by nuclear transmutation.
Understand radioactive decay kinetics. Be able to do problems involving radioactive
decay kinetics; understand dating of archeological objects using decay kinetics.
Understand and be able to calculate energy changes in nuclear reactions (nuclear
binding energies).
Understand the difference between nuclear fission and nuclear fusion.
8.
9.
Understand issues of health and safety with respect to radioactivity (biological effects).
Learn about some of the medical applications of radioactive isotopes.
6.
Japan Upgrades Fukushima Nuclear Accident to Top Level 7 Nuclear Event
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Nuclear Chemistry
Nuclear Chemistry
Nuclear chemistry involves changes to the nucleus of the atom, the protons and neutrons, there really is no traditional
“chemistry” involved. The energy changes are profound!
In radioactive decay a nucleus is transformed into a new nucleus by the emission of highly energetic particle(s) and
energy.
Nuclear reactions are used
to produce electricity
to date archeological objects
to cure diseases
to diagnose illness
in military strategies
However, the use of nuclear materials poses an environmental/waste-disposal challenge.
Chemical Reactions
Nuclear Reactions
Compounds are formed/decomposed. All
atoms remain intact.
Valance electrons involved.
Protons, neutrons and other particles are
involved. Valence electrons inconsequential.
Relatively small changes in electron energies.
No measurable mass change.
Enormous changes in energy.
Mass is not conserved.
Standard chemical kinetics applies.
All spontaneous reactions proceed towards
equilibrium.
Reaction rates (kinetics) not affected by T, P,
catalysts, etc.
There is no equilibrium.
Nuclear Chemistry
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Some History of Discovery
Becquerel
1896: Antoine-Henri Becquerel discovers uranium minerals emit some
type of radiation working with Marie and Pierre Curie.
½ 1903 Nobel Prize in Physics:
"in recognition of the extraordinary services he has
rendered by his discovery of spontaneous
radioactivity"
1898: Marie Curie discovers thorium minerals also emit some type of
radiation. Eventually discovers the radioactive elements polonium and
radium.
Marie Curie
½ 1903 Nobel Prize in Physics for the Curies:
"in recognition of the extraordinary services they
have rendered by their joint researches on the
radiation phenomena discovered by Professor Henri
Becquerel"
Pierre Curie
Full 1911 Nobel Prize in Chemistry:
"in recognition of her services to the advancement of
chemistry by the discovery of the elements radium
and polonium, by the isolation of radium and the
study of the nature and compounds of this
remarkable element"
These discoveries were followed by extensive research into radioactive
elements. A key question was, “What are the particles being emitted
from the elements?”
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Nuclear Chemistry
Most Common Types of Radioactive Decay
Of the three types of nuclear radiation, alpha and
beta are particles:
An alpha particle is a helium nucleus: 2 α
A beta particle is a high kinetic energy electron
emitted by an unstable nucleus. 0
4
-1
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β
Gamma radiation is electromagnetic radiation of
very high energy but no mass. 0
0
γ
Nuclear Chemistry
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Penetrating Power of Nuclear Radiation
The penetrating ability of each type of radiation is inversely proportional to the mass. The
higher the mass, the less ability to penetrate matter. However, biological damage done by the
radiation is proportional to the mass.
Alpha (α): poor penetrating power - greatest biological damage per particle, if ingested or
inhaled.
Beta (β): moderate penetrating power - moderate biological damage per particle.
Gamma(γ): high penetrating power - moderate to low biological damage per photon .
Nuclear Chemistry
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Measuring Radioactivity
Geiger counters are used to detect ionizing radiation (usually beta particles and gamma rays, but certain models can
detect alpha particles). An inert gas-filled tube (usually helium, neon or argon with halogens added) briefly conducts
electricity when a particle or photon of radiation makes the gas conductive. The tube amplifies this conduction by a
cascade effect and outputs a current pulse, which is then often displayed by a needle or lamp and/or audible clicks.
Modern instruments can report radioactivity over several orders of magnitude.
The Geiger counter’s efficiency depends upon the radiation
type. Which type of radiation do you think Geiger counters
are most efficient at detecting?
Another device used is a scintillation counter. A scintillation counter contains a phosphor that will emit a tiny flash of light
when radiation strikes it. For example, zinc sulfide will emit light when struck by alpha particles. The light is caused by
electronically excited electrons in the atoms of the phosphor as the electrons return to lower energy levels. The flashes
are magnified electronically and counted to measure the activity of the radiation source. Scintillation counters can be
used to detect radioactive emissions that are too weak to ionize atoms.
Nuclear Chemistry
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Terminology, Isotopic Notation & Equations
Nucleons: Protons and neutrons
Nuclide: The nucleus of a specific isotope of an element
mass #
p+n
Nuclide Notation:
14
6
Example carbon-14, C-14
C
atomic #
Z=p
Balancing Nuclear Equations:
Nuclear reactions must be balanced by mass number and
charge (atomic number). Nuclide notation is used to balance
nuclear reactions.
U→
235
92
14
6
Th + 24α
231
90
alpha emission by U-235
A new element is formed
C → 147 N + −10 β
beta emission by C-14
A new element is formed
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Nuclear Chemistry
Nuclear Equations and Transformations
Complete the following nuclear equations.
Beta, β, Radiation
(An electron is ejected from the nucleus, that’s strange!)
Th → ?+ −10 β
234
90
?→
214
84
214
83
Bi + β
0
−1
? → ?+ 24α
U → ?+ 5 24α
234
92
A neutron is transformed into a proton inside the nucleus. This
process produces a β particle.
1
0
n→?
Gamma, γ, Radiation
The nucleus is said to contain “nuclear” energy levels. Gamma
radiation occurs when a daughter nucleus is formed in an excited
energy state and then relaxes to the ground state. This is similar to
the Bohr model of light emission when electrons relax to the
ground state “electronic” energy level.
U→
238
92
Th* + 24α →
234
90
Th + 24α + 00 γ
234
90
*denotes a excited nuclear state
Nuclear Chemistry
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Other Types of Decay (not as common)
1.
Positron emission:
0
+1
e or
0
+1
β
(more commonly observed from artificially
synthesized elements: Am, Bk, Fm, etc.)
A positron is the “antimatter” particle to an
electron. Same mass but opposite charge.
207
84
•
Po →
Bi +
0
+1
?
Positrons have very short lives. Positrons
and electrons annihilate each other upon
contact. All mass is converted to energy!
0
+1
e + e → 2 γ
0
−1
7
4
•
e
To emit a positron, a proton is
transformed into a neutron within the
nucleus and the positron formed is
emitted immediately from the nucleus.
Atomic number DECREASES , mass
number is unchanged.
1
1p→
•
207
83
2. Electron capture
Here a low energy electron within the atom is captured
by the nucleus.
Be +
e →
7
3
Li + hv (x − ray)
Like positron emission, when capturing an
electron, a proton is transformed into a
neutron within the nucleus. Atomic number
DECREASES , mass number is unchanged.
(
•
0
−1
1
1
p+
0
−1
e →
1
0
n
)
Electron capture is accompanied by the
emission of x-rays. These high energy
photons are emitted as an electron makes a
transition from a higher energy orbital to a
now unfilled lower energy orbital.
Complete the following nuclear reactions:
0
0
13N→13C + ?
7
6
0
41
?+−1
e→19
K
Nuclear Chemistry
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22Na → 0β + ?
11
+1
U-238 Decay Series
A decay series is the series of
steps an unstable nucleus will
undergo before a stable
daughter nucleus is created.
Start here
U-238
Each α decay lowers the atomic
number by 2 and the mass
number by 4.
Each β decay increases the
atomic number by 1 with no
change in the mass number.
The kinetic half-life for each
decay is also given.
There are four naturally occurring
decay series: U-238, U-235,
Np-237 and Th-232.
End here
Pb-206
(109 yrs latter)
Nuclear Chemistry
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