During some nuclear reactions, the mass of the new atom
produced is usually slightly less than that of the reactants.
This is called the mass defect. The relationship between
the missing mass and the energy produced is given by the
formula E = mc2 (E=energy; m=missing mass; c=speed of
light)
• Energy is converted from mass
• Energy released is very high in comparison to ordinary
chemical reactions
• Fission and fusion are two types of nuclear reactions
that produce large amounts of energy
Fission is a form of a nuclear reaction in which a large nucleus is
split into smaller nuclei
• A large fissionable nucleus absorbs slow moving neutrons
• The large nucleus is split into smaller fragments and releases
more neutrons
• Tons of nuclear energy is released. Energy is converted from
mass.
• Energy released is less than in fusion reactions.
• In nuclear power plants, fission process is well controlled.
• Energy produced is used to produce electricity.
• In nuclear bombs, fission process is uncontrolled. Energy and
radiations released are used to cause destructions.
• Nuclear wastes are produced that are dangerous and pose
serious health and environmental risks.
• Nuclear wastes must be stored and disposed of properly.
1 n
0
+
235 U
92

91 Kr
36
+
142 Ba
56
+ 310n
Fusion is a form of nuclear reaction in which small nuclei are joined to
create a larger nucleus.
• Two small nuclei are brought together under extreme high
temperature and high pressure.
• The two nuclei are fused to create a slightly larger nucleus.
• Tons of nuclear energy is released. Energy is converted from mass.
• Energy released is much greater than that of fission reaction.
• Fusion produces no nuclear waste.
• Fusion reactions occur exclusively in the sun.
• High temperature and high pressure are required for fusion
reactions to occur. High temperature and pressure are necessary to
overcome the repelling of two positive nuclei that are to be joined
together.
1 H
1
+
2 H
1

3 He
2
Nuclear process Mass number
and equation
after decay
Alpha decay
226 Ra 
88
222 Rn + 4 He
86
2
Beta decay
14 C  14 N +
6
7
0 e
-1
4
same
Positron
Same
emission
226 Ra  226 Fr
88
87
0
+ 1e
Protons (atomic Neutrons after
number) after
decay
decay
2
2
1
1
1
1
Artificial Transmutation – bombarding nucleus with high speed particles
40 Ar
19
+
1 H
1
 +
40 K
19
+
1 n
0
Fission – nucleus splits into smaller nuclei; mass is converted to energy;
more energy than chemical reactions; produces dangerous radioactive
wastes
235 U
92
+
1 n
0

142 Ba
56
+
91 Kr
36
+ 310n
Fusion – nuclei join to make a larger nucleus; mass is converted to energy;
energy is more than fission; produce no radioactive waste; high energy and
high pressure needed to overcome repelling nuclei
2 H
1
+
2 H
1

4 He
2
+ energy
A nuclear equation is balanced when the sum of
masses and sum of charges are equal on both sides of
the equation.
222 Rn
86

4 He
2
+
218 Po
84
The equation above is balanced because the mass
number on the left (222) is equal to the masses on the
right (4 + 218 = 222). The charge on the left (86) is
equal to the sum of charges on the right (2 + 84 = 86).
An unbalanced nuclear equation is usually given as an
incomplete equation in which a particle is missing. An
example of an unbalanced nuclear equation is given
below:
X +
0 e
-1

37 Cl
17
What particle is X in the above equation?
Top mass number of X MUST add to 0 to equal 37.
Bottom charge number of X MUST add to -1 to equal 17.
37 X
18
- find the element with an atomic number of 18 on
the periodic table = Ar
37 Ar
18
+
0 e
-1

37 Cl
17
Write a balanced nuclear equation for plutonium-239
Step 1 Write nuclide symbol from Table N
Step 2 Write decay mode symbol
Step 3 Determine missing top #; bottom #; atom’s symbol
239 Pu
94

4 He
2
+
235 U
92
Practice
Write a balanced nuclear equation for iodine-131