Essential Question:
What distinguishes a nuclear reaction from an ordinary chemical reaction?
Nuclear Reactions & Ordinary Chemical Reactions
Regular chemical reactions involve only the out electrons of atoms. In a chemical reaction,
elements do not change from one to another.
2H2 + O2  2H2O
Nuclear reactions involve the atomic nucleus. When an atomic nucleus changes, it is very
probable that the products will be different elements than the reactants.
238
U 
92
234
Th
90
+
4
He
2
Many nuclei are radioactive. This means they are unstable and will decay by emitting a particle,
transforming the nucleus into another nucleus, or into a lower energy state.
A chain of decays takes place until a stable nucleus is reached.
Essential Question:
What types of radiation exist and how harmful are they?
Nuclear Symbols
Alpha particle, 
Beta particle, an electron, 
Neutron
gamma ray, energy
While all particles produced by the decay of an atomic nucleus have the energy to penetrate
substances, some particles have much more energy than others.
Essential Question:
How is a nuclear equation balanced?
o
o
When writing a nuclear equation, the sums of the mass numbers and atomic
numbers of the reactants must equal the sums of the mass and atomic numbers of
the products.
Students should check their equations by comparing the sums of the superscripts
and subscripts on each side of the equation.
Balancing Nuclear Equations Practice
1. Complete and balance these nuclear equations by supplying the missing particles:
a) 6629Cu  6630Zn + _____
b) 0-1e + _____  73Li
c) 2713Al + 42He  3014Si + _____
d) 8537Rb + _____  8235Br + 42He
2. Write nuclear equation for the alpha decay of
(a) 19278Pt
(b) 21084Po
3. Write nuclear equations for the beta decay of
(a) 23993Np
(b) 9038Sr
4. Determine the type of emission or emissions (alpha, beta, or gamma) that occurred in the
following transitions:
(a) 21082Pb to 210 82Pb
(b) 23491Pa to 23089Ac to 23090Th
(c) 23490Th to 23088Ra to 23088Ra
5. Complete and balance these nuclear equations by supplying the missing particles:
(a) 2713Al + 42He  3015P + _____
(b) 2714Si  0+1e + _____
(c) _____ + 21H  137N + 10n
(d) _____  8236Kr + 0-1e
Match the three types of emission with the following ideas. Each may be used once, more than
once, or not at all.
a) alpha
b) beta
c) gamma
___ 1. Two protons and two neutrons
___ 2. High speed electron
___ 3. Most penetrating power
___ 4.
4
2
He
___ 5. Higher energy than x-rays
___ 6. Must be stored in a lead container
___ 7. Helium nucleus
___ 8.
0
1 e
Complete the following nuclear equations:
59
1
56
1.
27 Co + 0 n  25 Mn + 
C 
2.
14
6
3.
99
42 Mo
4.
235
92
5.
40
19
14
7
N + 
  +
0
1 e
+
0
0
U   + 
K +  
40
18
(alpha decay)
Ar
Essential Question: How is the half-life of a radioactive element used to determine how much
of a sample is left after a given period of time?
Half-Life
The length of time it takes for one-half of the atoms of a radioactive nuclide to disintegrate.
Half-Life Table
Nuclide
Half-life
Decay Type
6
2
He
0.802 seconds
Beta-minus
1.3 minutes
Alpha and Gamma
12.3 years
Beta-minus
227
92
U
3
1
H
14
6
C
235
92
U
5730 years
7.1 x 10 8 years Alpha and Gamma
Many radioactive particles decay into
other radioactive particles, however, the
final product of radioactive decay will
always be a stable substance.
Uranium-238 goes through a long sequence
of decays before it finally becomes stable.
The 14 individual decays that lead from U238 to Pb-206 are shown here.
How many alpha particles
are released?
How many beta particles?
Beta-minus
HALF-LIFE PROBLEMS
1. An isotope of cesium (cesium-137) has a half-life of 30 years. If 1.0 mg of
cesium-137 disintegrates over a period of 90 years, how many mg of cesium-137
would remain?
2. A 2.5 gram 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 half-life of
strontium-90 is 28 years. In what year will only 0.625 grams of this strontium-90
remain?
3. Actinium-226 has a half-life of 29 hours. If 100 mg of actinium-226 disintegrates
over a period of 58 hours, how many mg of actinium-226 will remain?
4. Thallium-201 has a half-life of 73 hours. If 4.0 mg of thallium-201 disintegrates
over a period of 6.0 days and 2 hours, how many mg of thallium-201 will remain?
5. The half-life of isotope X is 2.0 years. How many years would it take for a 4.0 mg
sample of X to decay and have only 0.50 mg of it remain?
6. Selenium-83 has a half-life of 25.0 minutes. How many minutes would it take for
a 10.0 mg sample to decay and have only 1.25 mg of it remain?
7. Element-106 has a half-life of 0.90 seconds. If one million atoms of it were
prepared, how many atoms would remain after 4.5 seconds?
8. Three grams of Bismuth-218 decay to 0.375 grams in one hour. What is the halflife of this isotope?
HALF LIFE
GRAPHS
1.
What is the half life of the graphed
material? ____
2.
What mass of radioisotope will
remain after 9.0 hours? _____
3.
Plot the data from a substance
with a half-life of 1.5 hours.
Essential Question:
How are fission reactions different from fusion reactions?
o
o
Fission: heavy nuclei are split into lighter nuclei. Fission reactions are
relatively easy to control but produce radioactive wastes.
Fusion: light nuclei are combined to form heavier nuclei. Fusion reactions are
difficult to initiate and control but produce little radioactive wastes.
Fission
Fusion
Essential Question:
What are some modern uses of nuclear energy?

Medicine

Electricity

Carbon-14 dating