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Nuclear Chemistry
Radioactivity
• One of the pieces of evidence for the
fact that atoms are made of smaller
particles came from the work of
Marie Curie (1876-1934).
• She discovered radioactivity or
radioactive decay, the spontaneous
disintegration of the nuclei of some
elements.
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Radioactivity or
Radioactive Decay
• The property in which an unstable
nucleus gives off particles and/or
energy
• This changes the atomic number
(p+) and forms a new element
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Radiation
• The penetrating rays (energy or
particles) emitted by a radioactive
source
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Radioisotopes
• Unstable isotopes that undergo
radioactive decay
• Elements with atomic number 83
and up are radioactive
• Bismuth and beyond…..
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Nuclear Reactions vs.
Normal Chemical Changes
• “Normal” Chemical Reactions involve
rearranging atoms. The elements don’t
change.
• Nuclear reactions involve the nucleus
• The nucleus opens, and protons and
neutrons are rearranged
• The opening of the nucleus releases a
tremendous amount of energy that holds
the nucleus together – called binding
energy
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Mass Defect
• Some of the mass can be converted into
energy
• Shown by a very famous equation!
E=mc2
Energy
Mass
Speed of light
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Types of Radiation
• Alpha (α) – a positively
charged helium nucleus
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2
•Beta (β) – an electron
0
1
•Gamma (γ) – pure energy;
called a ray rather than a
particle
He
0
0
e

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Other Nuclear Particles
• Neutron
1
0
n
• Positron – a positive
electron
0
1
e
•Proton – usually referred to
as hydrogen-1
•Any other elemental isotope
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1
H
Penetrating Ability
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Balancing Nuclear Reactions
•In the reactants (starting materials –
on the left side of an equation) and
products (final products – on the right
side of an equation)
Atomic numbers must balance
and
Mass numbers must balance
•Use a particle or isotope to fill in the
missing protons and neutrons
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Nuclear Reactions
• Alpha emission
Note that mass number (A) goes down by 4
and atomic number (Z) goes down by 2.
Nucleons (nuclear particles… protons and
neutrons) are rearranged but conserved
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Nuclear Reactions
• Alpha emission
• Try this one:
Po – 210 undergoes alpha radiation
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Nuclear Reactions
• Beta emission
Note that mass number is unchanged and
atomic number goes up by 1.
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Nuclear Reactions
• Beta emission
• Try this one:
Uranium – 238 undergoes beta decay
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Nuclear Fission
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Nuclear Fusion
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Nuclear Reaction
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Nuclear Power Plants
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SO YOU SAY YOU WANT TO
MELTDOWN YOUR OWN POWER
PLANT? HERE’S YOUR CHANCE
TO PLAY HOMER SIMPSON.
Nuclear Power Pros and
Cons
• Lot’s of energy
• No green house
gases
• Uses very little
fuel
• Very small chance
of massive
disaster
• Potential target
for terrorists
• Nuclear waste
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Accidents can happen
• The worst nuclear accident in US history
occurred on Three Mile Island in PA 1979
• The reactor meltdown was caused by several
mechanical errors as well as human error
creating a coolant leak
• The reactor that had the melt down is no longer
in use. The other reactor is slated to remain in
use until 2034
• “London Calling” by The Clash is about this
accident
Chernobyl – April 1986
• Chernobyl Nuclear
Power Plant– Pripyat,
Ukraine; April 1986
• During a test, the
reactor received a
power spike, causing
several explosions
• Radiation was picked
up several hundred
miles away, prompting
the Soviet Union to
admit the accident, 3
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Japan – Fukushima Power
Plant March 2011
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Radiation Detection
• Film Badges – exposure of film measures
radiation exposure
• Geiger Counters- detect radiation through
electric pulses in ionized gas
• Scintillation Counters- measure radiation
from substances that emit visible light when
energy is absorbed
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Radiation Detection
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Uses of Radiation
• Radioactive dating can determine the
approximate age of an object
• There are many uses of radiation in the
medical field
– Detect and kill cancerous cells
– X-Rays
– Many others
• Disinfect foods
Personal Dose Chart
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Effects of Radiation on the Body
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Half Life
• Time it takes for ½ a sample to decay
• No two radioisotopes decay at the same
rate
• Can be as short as a few seconds or take
billions of years….
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Half Life
• Uranium-238 has a half-life of 4.5 billion
years. It’s stable ending element is lead
(Pb)
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Half Life
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Half Life
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Half Life
A 2.5 g sample of an isotope of
strontium-90 was formed in a 1960
explosion of an atomic bomb at Johnson
Island in the Pacific Test Site. The halflife of Sr-90 is 28 years.
a) How many years will it take for 0.625
grams of Sr-90 to remain?
b) What year will this be?
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Half Life
A 2.5 g sample of an isotope of
strontium-90 was formed in a 1960
explosion of an atomic bomb at Johnson
Island in the Pacific Test Site. The halflife of Sr-90 is 28 years.
a) How many years will it take for 0.625
grams of Sr-90 to remain? 56 years
b) What year will this be? 2016
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Half Life
• The half-life of an isotope is 3.0 years. If
20 mg of this isotope disintigrates over a
period of 12 years, how many mg of this
isotope will remain?
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Half Life
• The half-life of an isotope is 3.0 years. If
20 mg of this isotope disintigrates over a
period of 12 years, how many mg of this
isotope will remain?
•
2.5 mg
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