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Nuclear Chemistry
Throughout history people have tried to control the
chemical matter in their world. In order to do so, an
understanding of the nature of matter; its inner-workings
is of course necessary.
Nuclear Chemistry
The ultimate goal of changing lead to gold, as was the
alchemists’ ambition was never reached.
An understanding of the world of the nucleus is necessary,
and we are still engaged in that endeavor to this day.
Changes:
physical
To understand the nucleus and its
changes it is necessary to review
physical and chemical changes.
In physical changes such as melting or
boiling, the structure of the
molecules themselves does not the
change. As a result the chemical
formula remains the same, and in
general only gross physical
properties change.
Scientist agree:
Climate change happens!
Polar bears depend on ocean ice to
hunt seals. Polar bears may be extinct
within our lifetime
H2O(s)  H2O(l)
Changes:
physical
Illustrate the melting of ice with a
particle diagram:
Scientists agree;
climate change happens!
H2O(s)  H2O(l)
Physical Changes
Ex: H2O (s) + energy  H2O (l)
>Molecules arrangement with each other changes
>The physical properties change
>The chemical formula
and the composition
remains unchanged
The crystal structure of ice
breaks down, but its still H2O!
>Small energy
changes occur
Examples: Melting, dissolving ,etc.
Changes:
chemical
In chemical changes the molecular
structure itself is changed as the
atoms rearrange into new
combinations. As a result new
molecules are formed, with a
completely different chemical
formula and a host of new
properties, depending on the new
arrangement of atoms.
H 2 + O 2  H 2O
Changes:
chemical
This type of change may or may not
involve a transfer of electrons
between the atoms involved,
leading to a more stable
arrangement of electrons.
Do you recall that atoms lose or
gain electrons typically to become
like noble gases?
H 2 + O 2  H 2O
Changes:
chemical
Illustrate the reaction of hydrogen with
oxygen to form water using a
particle diagram: H’s
O’s
H 2 + O 2  H 2O
H 2 + O2
H 2O
Be sure to apply the law of conservation of mass
Chemical changes
Ex: H2 + O2  H2O + energy
>Atoms in the molecule rearrange
>A new substance formed
>A new chemical formula
and different composition
Happy
new molecules
of H2O!
>The physical AND chemical properties change
>Larger energy changes are involved
Examples: rusting, burning, etc.
So it is that in neither physical nor chemical
changes, has the nucleus’ arrangement of
neutrons and protons changed. The nucleus in a
sense is like the world of Dr. Seuss and the
whos. It’s a place unaffected by outside factors
like temperature and pressure.
The nucleus is as unaware of the changes that
occur in the chemical world outside, as we are of
the changes that occur within. It is a world
governed by unimaginably strong forces, the
likes of which we’ve only just begun to
understand.
Welcome to the strange world of nuclear chemistry
1 - Nuclear Changes
> Nuclear particles rearrange
Watch carefully below
Can you
spot a
neutron
changing
into a
proton?
In the example, an unstable
carbon 14 nucleus changes
into a stable Nitrogen 14
nucleus.
Nuclear Changes
> Nuclear particles rearrange
As nuclear particles rearrange radiation particles are
given off. In this case a beta particle is released.
Nuclear Changes
> Nuclear particles rearrange
Changes such as this nuclear decay,
involve nuclear particles changing forms:
In this case neutrons are changing into protons.
Nuclear Changes
> Nuclear particles rearrange
> Atomic number can change
and Old elements can change
into new elements
When the number of protons change
the atomic number and identity of the
element change
Nuclear Changes
> Nuclear particles rearrange
> Atomic number can change
and Old elements can change
into new elements
>Mass is converted into energy
(as Radiation)
The radiation that is given off comes
when matter is converted into energy.
The famous E=mc2 equation of
Einstein shows the relationship
Nuclear Changes
> Nuclear particles rearrange
> Atomic number can change
and Old elements can change
into new elements
> Mass is converted into energy
(as Radiation)
> Largest energy changes
Nuclear reactions like this fusion
explosion release much more energy
than even the most violent of chemical
changes.
Nuclear Changes
> Nuclear particles rearrange
> Atomic number can change
and Old elements can change
into new elements
>Mass is converted into energy
(as Radiation)
> Largest energy changes
A more useful nuclear change is fission, which can
provide huge amounts of electricity and doesn’t
contribute to climate change.
Nuclear Changes
> Nuclear particles rearrange
> Atomic number can change
and Old elements can change
into new elements
> Mass is converted into energy
(as Radiation)
> Largest energy changes
Examples: radioactive decay, fission, fusion
It has other undesirable consequences though.
Nuclear Stability
> Stability of the nucleus depends on ratio
between protons and neutrons
> Stable ratio is fairly equal
> (1proton :1neutron) in smaller atoms,
> About 1 : 1.3 ratio in larger atoms
Ex: Bromine 80 = 35 protons : 45 neutrons
Nuclear Stability
Ex: Carbon 12
6 protons
6 neutrons
Stable nucleus
Ex: Carbon 14
6 protons
8 neutrons
Unstable nucleus
Think of the nucleus like a blob of cookie dough. Not
enough water and dough crumbles, too much water and
its too runny to stay together. The nucleus requires a
particular ratio of protons to neutrons to be a stable unit.
The graphic below shows the numbers of neutrons and protons for
specific nuclides or C, N, Ne, and S
Explain, in terms of atomic particles why the S-32 shown in the graph is stable
Radioactivity: 1) Transmutation or “decay”
Many different kinds of radiation
Particles can be produced
Transmutation also known as “decay” occurs when
particles in an unstable nucleus break down
releasing a particle of radiation.
Radioactivity: Transmutation or “decay”
Many different kinds of radiation
Particles can be produced
> All atoms above atomic number 84 have an unstable
nucleus. In the illustration an unstable Uranium nucleus
decays, releasing a particle of radiation,
Radioactivity: Transmutation or “decay”
Many different kinds of radiation
Particles can be produced
Though Uranium releases neutrons, a variety particles of radiation are
released by other elements. These include alpha particles, protons, and
negative beta particles (like electrons from the nucleus!).
Pure energy can also be released in the form of gamma radiation.
Particles: Reference table O:
Alpha particles – (alpha decay)
> Largest particle, with mass of 4
and +2 charge
>Similar to helium nucleus: 2 He 4
>Greek symbol alpha α
upper: Mass #
Lower: Atomic #
(“nuclear charge”)
Ex: Alpha emitter:
Pu-234
240 
Pu
94
236 + He 4
U
92
2
Alpha
particle
This is a nuclear equation. In nuclear equations, the
atoms change, so an element present on one side, will
be a different element on the other side.
Ex: Alpha emitter:
Pu-234
240 
Pu
94
236 + He 4
U
92
2
Alpha
particle
Notice though,how the atomic numbers (charge #) and
mass numbers balance. More on this later!
Notice: unstable Plutonium loses 2 protons, becomes uranium
Beta particles (Beta Decay)
>Small particles with little mass
and -1 charge
>Similar to electron
>Greek symbol
β
0
e
-1
Notice the lower
Number is the charge
Beta Emitter: Carbon 14
14  N 14 +
C
6
7
0
e
-1
Beta radiation
Notice: Carbon loses a negative charge and ends up with
an extra proton (Atomic number 6 changes to 7) How?
A neutron loses a negative charge and becomes a proton!
Gamma Radiation
>Highest energy particle, similar to x -rays
>Has no apparent mass or charge (neutral)
>Symbol gamma: γ
No loss of charge or mass
means element doesn’t change
(Though its usually given off with
other particles)
Ex: Cobalt-60 emits gamma rays
in addition to beta electrons
Selected Radioisotopes
Shown in Table N
(radioactive, unstable)
Radiation forms
Try this problem: (we’ll do more of these. Later)
What particle is represented by X?
11
11
C B +X
Solution: Insert atomic numbers (from per. Table)
and missing mass numbers to balance
0
C  B + X
6
5
+1
11
11
0 mass and +1 charge?
In nuclear equations numbers must balance on both sides.
+6 nuclear charge on the left. We insert a +1 on the right to
balance.
The mass of 11 on the left balances with the 11 on the right.
The particle X must have a mass of zero.
Try this problem: (we’ll do more of these. Later)
What particle is represented by X?
11
11
C B +X
Solution: Insert atomic numbers (from per. Table)
and missing mass numbers to balance
0
C  B + X
6
5
+1
11
11
According to table O
It’s a positron
Anti-matter!
Produced in particle accelerator
0 mass and +1 charge?
Try one: But don’t peek!
Notice:
1) U-238’s mass decreases
by 4, nuclear charge
decreases by 2: Loss of
alpha particle +2He4
2) Th234’s mass stays same,
0 mass lost, but nuclear
charge increases by +1:
loss of -1 charge: -1e0 beta
particles.
3) Same change for Pa-234
turning into U-234
Penetration of particles
>Alpha’s are the largest
(mass of 4), so they
penetrate little
>Beta’s are smaller,
(mass of 0, like an
electron) penetrate
easier
>Gamma’s smallest
(pure energy), highest
penetration
Keep and eye peeled
for this paper, wood,
and concrete example
What stops the radiation?
Indian point nuclear power plant in Peekskill
What are the silos
made from? Why?
Separation of particles
>Alpha’s are positive,
deflected toward
negative plate
>Beta’s are negative,
deflect toward
positive side
>Gamma’s are
neutral,
undeflected.
This website shows animates the separation of particles
Can you tell which particle is which?
Test your learning
1) How are physical changes different from chemical
changes? How does the nucleus change during those
changes?
2) What are the main characteristics of nuclear changes?
3) What characteristic of an atom’s nucleus causes it to be
unstable?
4) What are the three naturally produced radiation forms?
What are their properties?
Click here to check out the crash course take on this topic
The energy released by a nuclear reaction results primarily from the
(1) breaking of bonds between atoms
(2) formation of bonds between atoms
(3) conversion of mass into energy
(4) conversion of energy into mass
The stability of an isotope is based on its
(1) number of neutrons, only
(2) number of protons, only
(3) ratio of neutrons to protons
(4) ratio of electrons to protons
Which of these types of radiation has the greatest penetrating power?
(1) alpha
(3) gamma
(2) beta
(4) positron
2- Half-life
>Radioisotopes decay at a special rate
>Used to age geologic and fossil samples
Example: (Ref Table H)
Radium 226
Half-Life = 1600 years
After Time
# half-lives
% sample
remaining
Fraction
remaining
Mass
remaining
0
0
100
all
½ left
10.00 g
After 2 half-life 25% of original
¼ left
2.50 g left
After 3 half-life 12.5% of original
1/8 left
1.25 g left
after1600 y After 1 half-life 50% of original
after 3200 y
+1600=
after
4800 y
+1600=
5.00 g left
Suppose that we start with 10 grams of Ra-222
Half-life time is
listed on
reference table N
Carbon-14’s ½ life is
5,700 years
Uranium-238’s ½ life is
4.5 billion years
Which would work
better to find the age
of ancient rocks?
(hint: the earth is
billions of years old!)
Answer: U-238. half–life closer to target age.
Graphing radioactive decay
Starting
mass.
After one
Half-life.
What fraction is left after the
second half-life?
Question: According to the graph, What is the half-life of Cesium 137?
Original sample is 100 grams, drops to 50 grams after 30 years.
Fraction remaining problems
Ex: What fraction of a sample of K-42
remains unchanged after 49.6 hours?
Ref. Table N: Half life K-42 = 12.4 hrs
Total time
Half-life time
49.6 hrs
= 4 half-lives
12.4 hrs
Fraction Remaining = (1/2)
4
(Number of half-lives)
= (1/2)
=½x½x½x½
= 1/16th
Or make a table:
time
0
7.2 sec
14.4 sec
21.6 sec
28.8 sec
36.0 sec
fraction remaining =
(1/2)5
(1/2)36/7.2
=½x½x½x½x½
fraction
all
1/2
1/4
1/8
1/16
1/32
Here’s another:
Based on the selected radioisotopes chemistry reference
table, what is the fraction of a sample of potasium-42
that will remain unchanged after 62.0 hours?
time
fraction
0
12.4 hrs
all
24.8 hrs
1/4
37.2 hrs
1/8
49.6 hrs
1/16
62.0 hrs
1/2
1/32
Nuclear Equations
Notice: 238 = 234 + 4
Ex: 92 U
238
Nuclear charge

Mass is conserved
234
Th
+
90
4
He
2
Mass
Notice: 92 = 90 + 2 charge is conserved
Nuclear equations can be balanced just like chemical
equations. The problem below illustrates the process.
Problem: What is the identity of X?
226
Ex: 88 Ra 226
88
=
?

=
X
?
+
4
+
4
He
2
+
2
222
X
86
Atomic number 86 = Radon
222
Rn
86
Test your learning
1) The half life of iodine-125 is 60 days. What fraction of iodine-125
nuclides would be left after 360 days?
2) A medical institution requests 1 g of bismuth-214, which has a half
life of 20 min. How many grams of bismuth-214 must be prepared if
the shipping time is 2 h?
3) Use reference table to write the nuclear equation for the decay of
iodine 131. What particle is emitted? What new element is
produced?
4) Radon 222 is produced by the decay of what radioisotope? Write a
balanced nuclear equation to find out:
0
+1
A positron
Regents exam question 79 - 81:
3 - Radioactivity: Artificial Transmutation
>Decay caused by bombarding nuclei with
outside radiation, in particle accelerators
Ex:
13
element
Al
27
+
2
He
4
Hit with radiation

15
P
30
+
0
n
1
Forms New element
(an Alpha particle)
In artificial transmutation, look for a radiation particle
on the left, reactant side. Particles to look for include
Protons or the like: 1 H 1 and Alpha particles: 2 He 4
And
more
Radiation
(a neutron)
Particle accelerators are used study
the structure the atom’s nucleus
> Particles are accelerated to a high speeds
And then collide into various samples.
Detectors help analyze the results.
This website is the particle adventure. What are
subatomic particles made of?
The strange world of sub-subatomic particles
Aka: What are Protons, neutrons and electrons made of?
(not on the regents exam, but who cares? Its weird, cool stuff!)
Elementary particles: Quarks (nuclear),
leptons (electron) & gluons (force
carriers)
6 Quark flavors:
up(+2/3 charge)
down (-1/3)
charm (+2/3)
strange (-1/3)
top (+2/3)
bottom (-1/3)
u(+2/3 )
u(+2/3 )
+ d(-1/3 )
+1
proton
Neutron
u(+2/3 )
d(-1/3 )
+ d(-1/3 )
0
FYI: particleadventure.org
2-4 aren’t even nuclear changes,
they’re chemical reactions!
An easy one, huh?
Radioactivity: Nuclear Fission
Fission = Splitting the atom’s nucleus
Releases large amounts of energy
Nuclear Fission
> A large nucleus is split into two smaller nuclei
More
Radiation
radiation
U fuel
2 products
Releases
energy
In a chain reaction, on neutron strikes a nucleus,
splitting it and releasing 3 neutrons. Each of the 3
strikes another nucleus, releasing a total of 9
neutrons. And so on. Imagine the consequences!
Chain Reaction 1  3  9  27  etc.
Mass is converted into energy
during nuclear changes
How nuclear power plants work
Left over
Nuclear
waste must
be stored.
Bad!
Radiation
Released
In the
reactor
Heats up
a fluid
Heat is
passed to
water
changing it
to steam
Electricity is
passed along
the grid to our
homes and
businesses
Steam under
pressure drives
A generator
(turbine) to
make electricity
steam condenses
back giving up its
heat passed back
to a nearby river
Nuclear Energy
Advantages
>No gas emissions like with fossil fuels
(leading to climate change)
>Lots of energy for small amount of fuel
Disadvantages
>Radioactive waste has long half-lives
-Remain dangerous for long periods
-Present long term storage problems
Nuclear Fusion
>Fusion = put together
>Two small nuclei combine into one
>Release huge amounts of energy
1H
2
3
4
1
+ 1 H  2 He + 0 n + energy
deuterium and tritium changed into Helium
Problem: Positive nuclei repel
must use small nuclei used to overcome forces
Extremely High temperatures required
Nuclear weapons: the H bomb
Aka: what good is a device that destroys everything?
TNT chemical bomb  fission bomb  fusion bomb
Test your learning
1) Write a nuclear equation showing natural transmutation
and an equation showing artificial transmutation.
Explain how they are different.
2) Describe one advantage of nuclear fission and one
disadvantage.
3) What advantage does nuclear fusion have over nuclear
fission? Why don’t we use nuclear fusion for energy
production?
Can you identify these changes?
Fission
Natural Transmutation (alpha decay)
Artificial Transmutation
Fusion
synthesis
decompostion
Artificial Transmutation
Natural Transmutation
(beta decay)
4 - Uses for Radioisotopes
Tracers – track chemical reactions
Ex: Photosynthesis with radioactive Oxygen tracer
CO2 + H2O + sunlight  C6H12O6 + O2
Where does the Oxygen we breath come from?
Notice where the O in O2 came from?
From the water! (not the CO2)
Industrial applications
Measuring thickness of material,
based on absorption of radiation
(thicker materials absorb more radiation)
Uses for Radioisotopes
Medical Treatments (short half-lives)
Technetium 99
– Diagnose brain tumors (tracer)
Iodine 131
– Treat thyroid disorders
Radium and Cobalt 60
– cancer treatment
Food Irradiation
kills bacteria and fungi,
prevents food spoilage
Geologic dating
U-238 to Pb-206 ratio –
dating rocks
C-14 to N-14 ratio – age
of fossils
Half-life determines its
application
Test your learning
1) What characteristic of a radioisotope is important for its
use in medical procedures?
2) What advantage does irradiated food have for
developing countries?
3) What radiation particle is emitted by Technetium 99,
allowing it be visible during a bone scan?
4) Why is uranium 238 used to date rock formations while
Carbon 14 is used for fossils?