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NUCLEAR CHEMISTRY
FYI: Historical Perspective
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Henri Becquerel
1896 - Discovers
natural radioactivity
FYI: Historical Perspective
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Marie Sklodowska, Polish
chemist marries Pierre Curie,
French physicist
Marie died from leukemia
caused by her exposure to
radiation
Pierre was killed while crossing
the street when he was hit by a
vegetable wagon.
FYI: Historical Perspective
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Ernest Rutherford
1899 – Discovers alpha,
beta and gamma radiation
Nuclear Reactions
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Involve changes in the composition of nuclei
Accompanied by the release of tremendous
amounts of energy
Two types:
–
–
Nuclear fission
Nuclear fusion
Nuclear Fission

The splitting of a heavy nucleus into lighter
nuclei
Nuclear Fusion
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The combination of light nuclei to produce a
heavier nucleus
Nuclides
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Different atomic forms of all elements

Most small nuclides have equal # of
protons and neutrons

Some nuclides have “magic #’s” of protons
and neutrons and are especially stable
The neutron-to-proton ratio determines
the stability of the nucleus

For low atomic #’s:
–
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Equal #’s of protons and neutrons
Above atomic #20 (Calcium):
–
More neutrons than protons
Nuclei whose neutron-to-proton ratio is
unstable undergo radioactive decay by emitting
1 or more particles and/or electromagnetic rays:
Nuclei whose neutron-to-proton ratio is
unstable undergo radioactive decay by emitting
1 or more particles and/or electromagnetic rays:
Type/
symbol
Alpha
4
Identity
Mass Charge Penetration
(amu)
 or 2 He
helium
nucleus
4.0026
2+
low
0
-1
 or e
electron
0.00055
1-
low-med

0
high
Proton 1p or 1H
1
1
high energy
0
radiation
proton,
1.0073
H nucleus
1+
low-med
Neutron
neutron
0
very high
Beta
Gamma
0
0
1
0
n
1.0087
Comparing penetrating ability (lowhigh) and SHIELDING…
or thin
piece of metal
or block of lead
Geiger counter

Device used to
measure the total
amount of radiation a
person has received
Nuclear Equations
for
Radioactive Decay
Alpha Particle Decay

Example 1: Radium-226 transmutates by alpha decay.
Write the nuclear equation that represents this process.
226
88
Ra
222
86
Rn  
or
226
88
Ra
222
86
Rn He
4
2
*the atomic
number will
change because
of changing
proton #, so it is
a new element
and symbol
*the math must
equal on both
sides
Beta Particle Decay
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Example 2: Write the nuclear equation for the
beta-decay of boron-12.
12
5
B C  
12
6
or
12
5
B C  e
12
6
0
1
In β− decay, the
weak interaction
converts a neutron
into a proton while
emitting an electron
*the math must
equal on both
sides
Gamma Radiation

Example 3: Write the nuclear equation
representing gamma radiation given off by the
unstable radionuclide cobalt-60.
Nuclear Fission & Fusion
FISSION: a heavy nucleus splits into 2
lighter nuclei
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some elements undergo fission
spontaneously
some elements can be induced to undergo
fission when bombarded with other particles
(e.g. neutrons)
Nuclear Fusion (think stars)
"Every time you look up at the
sky, every one of those points
of light is a reminder that
fusion power is extractable
from hydrogen and other light
elements, and it is an
everyday reality throughout the
Milky Way Galaxy."
Carl Sagan, Spitzer Lecture,
October 1991
FUSION: 2 nuclei combine to form a
heavier nucleus

the sun is a tremendous fusion reaction; the
major fusion reaction in the sun is thought to
be:
H H He  n  energy!
2
1

3
1
4
2
1
0
both fission & fusion release large amounts
of energy (fusion more than fission)
The Atomic Bomb
(FISSION)
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when the nucleus of U-235 splits, 2 isotopes are
formed, plus neutrons are emitted
these neutrons collide with other U-235 atoms,
causing them to undergo fission; they release
neutrons, and so on…
The result - CHAIN REACTION!!
The CRITICAL MASS is the minimum mass of
fissionable material that must be used to sustain
a chain reaction
The Atomic Bomb (FISSION)
The Atomic Bomb (FISSION)
Atomic Bomb
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Little Boy was the first
nuclear weapon used in
warfare. It exploded
approximately 1,800 feet
over Hiroshima, Japan, on
the morning of August 6,
1945, with a force equal to
13,000 tons of TNT.
Immediate deaths were
between 70,000 to
130,000.
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Fat Man was the second nuclear
weapon used in warfare.
Dropped on Nagasaki, Japan,
on August 9, 1945, Fat Man
devastated more than two
square miles of the city and
caused approximately 45,000
immediate deaths.
While Little Boy was a uranium
(U-235) gun-type device, Fat
Man was a more complicated
and powerful plutonium (Pu-239)
implosion weapon that exploded
with a force equal to 20 kilotons
of TNT.
Nuclear Power Plants (use nuclear
reactions to generate electricity)
*nuclear reactor
*San Onofre, Ca Nuclear Generating Station.
Situated near a body of water to use the water…
TO GENERATE ELECTRICITY:
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The energy released in the fission process
generates heat, some of which can be
converted into usable energy.
This heat is used to boil water to produce
pressurized steam.
Steam turns turbine of a generator.
Generator makes electricity.
Nuclear Power Plants contain
nuclear reactors
http://science.howstuffworks.com/nuclear-power3.htm
Nuclear Reactors (FISSION)
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use subcritical masses of fissionable material
(below the mass to create chain reactions)
CORE of reactor: contains fuel pins made of
U-235; interspersed among the pins are control
rods
control rods: absorb neutrons (regulates
amount of energy produced)
– pull rods out of core: fission increases
(more energy in core)
–
push rods back into the core: fission decreases (less
energy in core)
Safety feature:
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if power is lost, rods will automatically fall
into the core and shut the reaction down.
Water pumps help to prevent the
overheating of the reactor core (can
trigger an explosion: Chernobyl)
PROS OF NUCLEAR ENERGY:
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no air pollution
enormous amt. of energy released
alternative to using our rapidly decreasing
fossil fuels
CONS OF NUCLEAR ENERGY
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containers for waste products may erode
or break
thermal pollution (heated water returned to
rivers, etc.)
potential theft of fuel (Pu-239) for use in
weapons
VIDEO: Minutes to Meltdown
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Three Mile Island
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The movie The China Syndrome came out right
before the accident occurred at the Three Mile Island
nuclear reactor.

“the China Syndrome” means an explosion so
powerful it would blow a hole all the way to China
(which is directly on the other side of the Earth from
us in the United States)
NOTES (CP)
(Honors = slide #55 )
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Half-life and radioactivity
Half-Life 25.2
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Half-life (t1/2):
–
The half-life of a sample of a radioactive
isotope is the time required for half of it to
decay
–
After each half-life, half of the existing
radioactive atoms have decayed into atoms of
a new element.

Use half-lives of some radioisotopes found in
nature to determine the age of ancient
artifacts
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The half-life of Uranium-238 = billions of
years
Radioactive Decay of an Unstable
Isotope
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See textbook pg. 804
Questions
–
1. What percent of the atoms remains after 1 halflife?
50%
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2. What percent of the atoms remains after 2
half-lives?
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25%
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3. Approximately how many half-lives does it
take for 12.5% of the radioisotope to remain?
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Three half-lives
Question
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Compared to the energy liberated per gram
during a typical chemical reaction, the
amount of energy liberated per gram during
the decay of a radioisotope is:
A. somewhat greater
B. less
C. much greater
D. about the same
Answer
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C. much greater
Do #51 on pg. 822 of text
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Decay curve for thorium-234
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A. what percent of the isotope remains after 60
days?
B. How many grams of a 250 g sample of thorium234 would remain after 40 days had passed?
C. How many days would pass while 44 g of
thorium-234 decayed to 4.4 g of thorium-234
D. What is the half-life of thorium-234?
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Answers
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A. about 20%
B. about 85 g
C. about 83 days
D. about 25 days
Half-life CALCS
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Carbon-14 emits beta radiation and decays
with a half-life of 5730 years. Assume you
start with a mass of 2.00 x 10-12 g of
carbon-14
a. How long is 3 half-lives?
ANSWER
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A. 3 half-lives = 3 x 5730 years = 17,190 yrs

Carbon-14 emits beta radiation and decays
with a half-life of 5730 years. Assume you
start with a mass of 2.00 x 10-12 g of
carbon-14
b. How many grams of the isotope remain at
the end of 3 half-lives?
ANSWER
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B. the initial mass of carbon-14 is reduced by
one half for each of the 3 half-lives, so for 3
half-lives:
Remaining mass = 2.00 x 10-12 g x ½ x ½ x ½ =
0.250 x 10-12 g
= 2.50 x 10-13 g
Example #1
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Manganese-56 is a beta emitter with a halflife of 2.6 hours.
–
What is the mass of manganese-56 in a 1.0 mg
sample of the isotope at the end of 10.4 hours?
Answer
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10.4 hours/(2.6 hours/half-life) = 4 half-lives
1.0 mg x (½ x ½ x ½ x ½) = 0.063 mg Mn-56
Ex #2
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A sample of thorium-234 has a half-life of
24.1 days. Will all the thorium undergo
radioactive decay in 48.2 days?
Explain
ANSWER
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48.2 days/(24.1 days/half-life) = 2 half-lives
NO!!!
(½ x ½ ) or ¼ of the sample will remain.