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Nuclear Chemistry
Nuclear Power Plant in Richland, WA
The Band of Stability
• Certain isotopes are
more stable than others
• The ratio of protons to
neutrons is important in
determining stability
• Example: Mg has 12
neutrons and 12
protons, U has 146
neutrons for 92 protons
• Elements on the edge of
the band or outside of the
band are radioactive.
• Radioactive isotopes
usually have more than
83 protons.
What holds the nucleus together?
– Strong nuclear force (attractive)
– Force pushing protons apart = repulsion due to
positive charge (electrostatic force)
• Protons: contribute to both the attractive force
(strong force) and repelling force (charge)
• Neutrons: contribute to the strong force
(attractive) while having no charge. Act as the
“glue” to bind the nucleus together
Binding Energy: Energy needed to hold
the protons in the nucleus together (Also the
energy released when an atom is split).
Mass and energy
• During nuclear reactions, there is actually a small
change in mass
238.0003 g
238
92
U
233.9942 g + 4.0015 g = 237.9957
234
90
Th
4
+
2
He
Mass Defect: Measured mass of an atom
is LESS THAN the sum of the masses of its
particles.
E=
2
mc
Binding Energy
Mass
Speed of Light
How can we form a new element?
– Must have a stable nucleus and exist long
enough to be detected.
– The neutron to proton ratio is an important
factor in determining the stability of a
nucleus.
– Some isotopes are more stable than
others. Unstable isotopes undergo nuclear
decay to produce atoms with lower mass.
Nuclear Chemistry!
Nuclear chemistry: the study of
the nucleus of the atom.
(so, it involves neutrons and
protons, not electrons!)
Chemical vs. Nuclear Reactions
Chemical Reactions: # of atoms of each
element remains unchanged
Example: 2H2 + O2  2H2O
Nuclear Reactions: Affect the
nucleus of the atom—
rearrangements of protons and
neutrons.
**Sometimes the
rearrangements lead to unstable
or radioactive elements.
Radioactive Decay—Spontaneous
breakdown of an atom which results in the
emission of particles, energy or both.
Stability is relative
• Some radioactive elements
take thousands or millions of
years to decay
• Some radioactive elements
take days, minutes, or
fractions of a second to decay
Radioactive decay is measured in
Half-lives
Half-life: length of time it takes for half of a
starting amount of an element to decay
Ex. Radium has a half-life of 1,620 years
How many
years?
100 Radium
atoms
1620 years
50 Radium
atoms
1620 years
25 Radium
atoms
Half-life cont.
A shorter half-life means an element is more
radioactive because the radioactivity is
released faster.
Ex. Which element is more radioactive?
Carbon-14 (half-life 5,720 years) or Radium226 (half-life 1,620 years)?
Radium-226
Your turn!
You have a sample of 200 radioactive atoms
and the half life is 20 years. After 100 years,
how many atoms will be left?
100/20 = 5 half lives
200  100  50  25  12.5  6.25 atoms
(SO 6 ATOMS because you can’t have
0.25 of an atom!)
Real World use of
Half-Lives:
Radioactive Dating
• Ratio of carbon 12 to
carbon 14 used to
determine age of onceliving things! (Carbon14 has a half-life of
5,730 years)
• Uranium-238 has a
half-life of 4.5 billion
years so is used to date
rocks
3 types of Radiation
•Alpha (a) Radiation
•Beta (b) Radiation
•Gamma (g) radiation
Types of Decay: The Particles
1. Alpha
4
2
Alpha particle:
two protons and
two neutrons
positive charge
Same as
a Helium
nucleus
Alpha particles are so large they
cannot penetrate very far into matter
(they can be shielded with a piece of
paper!!)
Tho-Radia Face Cream
Promising instant curative and beautifying effects, Tho-Radia gained wide popularity in
France during the early 1930's as a range of beauty products and perfumes. The face
cream was especially popular and contained of 0.5g thorium chloride and 0.25mg
radium bromide per 100g. It was even advertised as a creation of ‘Dr. Alfred Curie'
although he was not a member of the Curie family and probably never existed.
http://www.environmentalgraffiti.com/offbeat-news/10-radioactive-products-that-people-actually-used/1388
Manufactured from 1918 to 1928 by the Bailey
Radium Laboratories, Radithor was a well-known
patent tonic that consisted of triple distilled water
containing at a least one microcurie of Radium 226
and 228 isotopes. Said to cure stomach cancer
and mental illness, it was even advertised as
‘Perpetual Sunshine' until it gained notoriety when
Eben Byers, an American industrialist, drank a
bottle a day for four years and consequently died
in excruciating pain as cancer of the jaw caused
his facial bones to disintegrate.
Radioactive Drinking Water
Ceramic jars that added radon
to drinking water were popular
during the early part of the 20th
century. Revigator advertised
itself as ‘nature's way to health'
and its ores gave off millions of
tiny rays of radiation that
penetrated the water, creating
‘healthful radioactive water'.
Radioactive Toy Set
The Atomic Energy Lab
first went on sale in 1951
and featured low levels
of genuine radioactive
material for children to
experiment with. It
remained on sale until
the late 1970's and
although the materials
were labeled as ‘safe'
you wouldn't find many
parents today willing to
let their kids play with
uranium ore.
Radium Chocolate
Radium Chocolate manufactured by Burk
& Braun was sold in Germany from 1931 to
1936, advertised for its powers of
rejuvenation.
Types of Decay: The Particles
2. Beta
0
-1
negative charge
An electron is emitted and a neutron is
converted into a proton!
beta particles =
high energy
electrons
Beta particles also are a bit too large to
penetrate you, and can be stopped
with aluminum foil.
Types of Decay: The Particles
3. Gamma—high energy radiation
• High energy electromagnetic radiation
• No mass or charge
• Often emitted along with beta or alpha radiation
Gamma rays penetrate, but can be
stopped with lead (like x-rays!)
Alpha Decay
• Atom releases an alpha particle.
• Atomic # decreases becoming new element.
238
92
U
234
90
Th
+
4
2
He
alpha particle
Notice:
• total starting mass equals total resulting mass: 238 = 234 + 4
• total starting charge equals total resulting charge: 92 = 90 + 2
Conclusion: in alpha decay a nucleus splits into
two smaller elements, one of which is always a
helium nucleus
Balancing Nuclear Equations
Your turn!
210
84
Po
Alpha Decay
4
2
206
+
82
Pb
Beta Decay
• Atom releases a beta particle with zero mass & negative charge
• Atomic number increases (becomes new element!)
14
6
C
14
7
N
+
Notice:
• total mass stays the same: 14 = 14 + 0
• total charge stays the same: 6 = 7 - 1
0
1
e
Balancing Nuclear Equations
Beta Decay
27
Si
14
0
-1
27
+
An electron is emitted and a neutron is
converted into a proton!
15
P
More Practice!
Francium-221 undergoes alpha decay.
Write the nuclear reaction below.
221
Fr
4
217
α + At
2
85
87
Thorium-234 emits a beta particle. Write the
nuclear reaction below.
234
234
0
Th
β + Pa
90
91
-1
The road to stability may be
long!
Things to notice:
-There are multiple steps
-some steps are alpha decay,
some are beta decay
- the stable end point is an
element with atomic # less than
83 (lead)
- there are also unstable lead
isotopes which are
intermediates
What are some uses for radioactive elements??
Nuclear
Medicine
Atomic
Weapons
Nuclear Power
Radiation Therapy
• Used to treat cancer (but yes, too much radiation
can actually CAUSE cancer)
• Mechanism: Radiation beams knock off
electrons from atoms making up DNA chains and
turn them into free radicals (damaging them!)
• Polonium, Cobalt, Cesium & Radium are all
elements used in radiation therapy.
Nuclear Power
• Fission—Splitting of a heavy nuclei (like Uranium)
**The products are radioactive.
Fission
• Splitting one nucleus into smaller fragments
• Nuclear power plants and most nuclear
weapons rely on nuclear fission
Nuclear Power
• Fusion—Combining of 2 or more light nuclei (H + H
 He) **Non-radioactive products. **Requires
extremely high temperatures (sun/stars)
Both release LARGE amounts of ENERGY!
What is a Chain Reaction?
Chain Reaction: A
reaction in which
the material that
starts the reaction is
also one of the
products and can
start another
reaction.
http://video.google.com/videoplay?docid=407619013941956006
Fusion
• Two nuclei combine
• Release large amounts of
energy, but requires very
high temperatures
– At such high temperatures, nuclei are
moving so fast that collisions between them
can overcome the natural repulsion of their
positive charges.
• Examples
– The Sun
– The Hydrogen bomb
Review: Splitting Atoms Releases
Neutrons, Making Heat
Heat
Neutrons
Heat Produces Steam,
Generating Electricity
Steam
Generator
Steam
produced
Turbine
Electricity
Heat
ATOMIC WEAPONS
What are they?
Nuclear weapons derive their destructive force
from nuclear fusion or fission.
How many have there been?
Two nuclear weapons have been detonated—both
by the United States at the end of World War II.
Where were these weapons dropped?
Hiroshima
• August 6th, 1945
• Uranium
• 140,000 people killed (instantly,
or from illness associated with radiation)
Nagasaki
• August 9th, 1945
• Plutonium
• 80,000 people killed (instantly, or from illness associated
with radiation)
Manhattan Project
(1941-1946)
• The project to develop the first nuclear weapon
during WWII (U.S., Canada & the U.K.)
• Robert Oppenheimer: Scientific researcher
(Father of the Atomic Bomb)
• 1945—Trinity Test (First
detonation of a nuclear bomb) in
New Mexico http://www.youtube.com/watch?v=
RqyBzXYZPoM&feature=fvsr
http://www.youtube.com/watch?v=Ru2PW
mGIoB8
2 Main Types of Nuclear Weapons:
#1: Nuclear Fission—(Atomic Bombs)
2 Main Types of Nuclear Weapons:
#2: Nuclear Fusion—(Hydrogen Bombs)
• Use the energy of a fission bomb to heat
the fusion fuel
• Over 1,000 times more powerful than a
fission bomb!
• Only 6 countries have detonated one:
U.S., Russia, U.K., China, France, and India
Nuclear Fallout—What is it?
Nuclear fallout: the residual radiation hazard
from a nuclear explosion, so named because it
"falls out" of the atmosphere into which it is spread
during the explosion.
http://todayspictures.slate.com/inmotion/essay_chernobyl/
Hotter stars will produce larger
elements
“Big Bang” = H & He
• Cooler Stars = fuse H
atoms into He
• Bigger/Hotter stars =
slightly heavier elements
made, up to Fe
• Supernova (explosion of
star) = create heaviest
elements (up to U)
Video clip: minutes 55:30 to 58
Nucleosynthesis: forming new elements
– Some light to medium12
8
4
+
sized elements formed by 4
6
2
simple fusion of two
Note: to find the product of a fusion reaction,
elements
Add up the mass #’s and atomic #’s of your
Be
C
He
starting elements
– Elements heavier than
iron are believed to be
made by neutron
capture. This is a twostep process
1. Neutron collides and fuses
with the nucleus of an atom
2. When the nucleus is
overloaded with these
neutrons, it will undergo
beta decay (a neutron
will turn into a proton)
Example from p92 in book
Step 1: Fusion with neutrons
63
29
Cu
+ 1n + 1n
0
0
65
29
Cu
Step 2: beta decay, creation of proton
65
29
Cu
0
1
e
+ 65 Zn
30