Nuclear Chemistry
Fusion and Fission
Nuclear Fission
• The splitting of a nucleus into smaller
fragments is called nuclear fission.
• Heavy atoms (mass number>60) tend to
break into smaller atoms, thereby
increasing their stability.
• Nuclear fission releases a large amount
of energy.
Nuclear Fission
The Fission Process
A neutron travels at high speed towards a uranium-235
nucleus.
1
0
n
235
92 U
The Fission Process
A neutron travels at high speed towards a uranium-235
nucleus.
1
0
n
235
92 U
The Fission Process
A neutron travels at high speed towards a uranium-235
nucleus.
1
0
n
235
92 U
The Fission Process
The neutron strikes the nucleus which then captures the
neutron.
1
0
n
235
92 U
The Fission Process
The nucleus changes from being uranium-235 to
uranium-236 as it has captured a neutron.
236
92 U
The Fission Process
The uranium-236 nucleus formed is very unstable.
It transforms into an elongated shape for a short time.
The Fission Process
The uranium-236 nucleus formed is very unstable.
It transforms into an elongated shape for a short time.
The Fission Process
The uranium-236 nucleus formed is very unstable.
It transforms into an elongated shape for a short time.
The Fission Process
It then splits into 2 fission fragments and releases
neutrons.
1
0
n
1
0
n
1
0
n
141
56 Ba
92
36 Kr
The Fission Process
It then splits into 2 fission fragments and releases
neutrons.
1
0
n
1
0
n
1
0
n
141
56 Ba
92
36 Kr
The Fission Process
It then splits into 2 fission fragments and releases
neutrons.
1
0
n
1
0
n
1
0
n
141
56 Ba
92
36 Kr
The Fission Process
It then splits into 2 fission fragments and releases
1
neutrons.
0n
141
56 Ba
1
0
92
36 Kr
1
n
Energy
Nuclear Fission Examples
235
1
141
92
1
235
1
138
96
1
U
n
+
92
0
U
n
+
92
0
Ba
Kr
n
3
+
+
56
36
0
Cs
Rb
n
2
+
+
55
37
0
Review:
Balancing Nuclear Equations
• Mass numbers and Atomic numbers must
add up on both sides of the reaction arrow.
256
140
112
46
1
Pd
• 100Fm  54Xe + ____ + 4 0n
For Atomic numbers 100 = 54 + X
X = 46
For Mass Numbers: 256 = 140 + X + 4
X = 112
White Boards
Supply the missing atomic symbol to
complete the equation for the following
nuclear fission reaction.
1n
0
+
235U
92
137Te
52
+ ?X + 2 1n + energy
?
0
18
Solution
1n
0
+
235U
92
137Te
52
+ 97Zr + 2 1n + energy
40
0
19
Fission Chain Reactions
• One fission reaction can lead to more
fission reactions in a process called a
chain reaction.
• Example - The fission of Uranium-235
Chain Reaction of Uranium-235
• A chain reaction can only occur if the starting
material has enough mass to sustain a chain
reaction. This amount is called the critical mass.
• Nuclear Fission is what occurs in Nuclear
Reactors and Atomic Bombs.
• The Nuclear reactor is a controlled fission
reaction, the bomb is not.
• The chain reaction releases a large amount heat
and energy that produces an atomic explosion.
Nuclear Fusion
• The combining of atomic nuclei to form a larger
atom is called fusion
• Nuclear fusion occurs in the sun when two nuclei
with low mass numbers combine to produce a
single nucleus with a higher mass number.
• Fusion releases large amounts of energy.
• Example:
1
4 1H + 2
0e
-1

4
2
He + energy
Energy
Nuclear Fusion
The Fusion Process
2
1H
3
1H
The Fusion Process
2
1H
3
1H
The Fusion Process
2
1H
3
1H
The Fusion Process
2
1H
3
1H
The Fusion Process
The Fusion Process
The Fusion Process
The Fusion Process
The Fusion Process
1
0
4
2 He
n
The Fusion Process
1
0
4
2 He
n
The Fusion Process
1
0
4
2 He
n
The Fusion Process
1
0
4
2 He
n
Nuclear fusion is what
powers our sun - and all
stars.
And also - Hydrogen Bombs
Fusion
• Fusion reactions also release very large
amount of energy but require extremely
high temperatures to start.
• Nuclear fusion also occurs in new stars
and is how all of our elements were made.
4
2
4
2
He +
He +
4
2
He 
8
4
Be 
8
4
Be + energy
12
6
C + energy
Other Fusion Reactions
• Hydrogen Bomb or possible Fusion
nuclear reactor reaction
•
3H
1
+ 12H 
4He
+ 10n
2
• New elements discovered:
• 20Ca + 95Am  115Uup
•
115Uup

113Uut
4
+ 2He
Remember:
Nuclear fission and fusion
both occur with an incredible
release of energy.
Energy
Learning Check
Indicate if each of the following describes
1) nuclear fission or 2) nuclear fusion.
___ A. a nucleus splits.
___ B. large amounts of energy are released
___ C. small nuclei form larger nuclei.
___ D. hydrogen nuclei react.
___ E. several neutrons are released.
Solution
Indicate if each of the following is
1) nuclear fission or 2) nuclear fusion.
1 A. a nucleus splits.
1, 2 B. large amounts of energy are
released.
2 C. small nuclei form larger nuclei.
2 D. hydrogen nuclei react.
1 E. several neutrons are released.
44
Chemical
Reactions
• Involve changes in
electrons
– Acids & Bases,
combustion, displacement
Nuclear
Reactions
• Involve changes in the
nucleus
– Nuclear fusion, nuclear
fission
• The same atoms appear
on both sides of the
reaction.
• New atoms appear as
products of the reaction.
• Small amount of energy
generated
• Large amount of energy
generated
– Burning fossil fuels
– 1 million times more than
chemical reactions
– Nuclear fusion on the sun
– Nuclear fission for reactors
Decay vs. Nuclear Reactions
• Alpha, beta, and gamma • Nuclear reactions involve
decay occur as ONE
more than just getting rid of
atom tries to increase
a few protons or neutrons.
The new atoms produced
it’s stability by getting
rid of a few neutrons, or
are VERY different
protons & neutrons.
elements than the reactant.
• The product is an alpha, • Nuclear reactions must be
beta, or gamma particle
started, so there are 2
and ONE new atom.
things on the left hand side.
There is only ONE thing
– Nuclear fission: makes 2
on the left hand side.
or more much smaller
atoms
– Nuclear fusion: makes 1
much larger atom
Nuclear Fission
Alpha Decay
What are the differences between the 2 above
nuclear equations??