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Chapter 19
The Nucleus:
A Chemist’s View
Section 19.1
Nuclear Stability and Radioactive Decay
Review
 Atomic Number (Z) – number of protons
 Mass Number (A) – sum of protons and neutrons
A
Z
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X
2
Section 19.2
The Kinetics of Radioactive Decay
4 Forces in Nature
Force
Equation
notes
Gravity
F = G m1 m2/r2
Works at an infinite
distance. Weakest of all
forces.
Electromagnetic
F = K q1 q2/r2
Works for short distances,
Holds the atom together.
Strong Nuclear force
E =mc2 (mass defect)
This is the glue that holds
the nucleus together.
Weak nuclear force
The force responsible for
radioactivity. Pulls the
nucleus apart.
Section 19.2
The Kinetics of Radioactive Decay
Stable nuclei
 When the strong force is greater than the weak
force the nucleus is stable.
 No nucleus beyond lead is stable indefinitely.
 Iron has the most stable nuclei.
 Most atoms have examples of stable and unstable
nuclei
Section 19.1
Nuclear Stability and Radioactive Decay
The Zone of Stability
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Section 19.1
Nuclear Stability and Radioactive Decay
Unstable nuclei
 When the weak force is greater than the strong
force the nucleus is unstable.
 Unstable nuclei become stable by changing the
make up of their nucleus
 This process is known as radioactive decay.
Section 19.1
Nuclear Stability and Radioactive Decay
Radioactive Stability
 Nuclides with 84 or more protons are unstable.
 Light nuclides are stable when Z equals A – Z
(neutron/proton ratio is 1).
 For heavier elements the neutron/proton ratio
required for stability is greater than 1 and increases
with Z.
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Section 19.1
Nuclear Stability and Radioactive Decay
Radioactive Stability
 Certain combinations of protons and neutrons seem
to confer special stability.
 Even numbers of protons and neutrons are more
often stable than those with odd numbers.
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Section 19.1
Nuclear Stability and Radioactive Decay
Radioactive Stability
 Certain specific numbers of protons or neutrons
produce especially stable nuclides.
 2, 8, 20, 28, 50, 82, and 126
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Section 19.1
Nuclear Stability and Radioactive Decay
Types of Radioactive Decay
 Alpha production (α):
 Beta production (β):
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Section 19.1
Nuclear Stability and Radioactive Decay
Types of Radioactive Decay
 Gamma ray production (γ):
 Positron production:
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Section 19.1
Nuclear Stability and Radioactive Decay
Types of Radioactive Decay
 Electron capture:
Inner-orbital electron
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Section 19.1
Nuclear Stability and Radioactive Decay
Decay Series (Series of Alpha and Beta Decays)
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Section 19.1
Nuclear Stability and Radioactive Decay
CONCEPT CHECK!
Which of the following produces a  particle?
a)
68
31
b)
62
29
c)
212
87
d)
129
51
Ga +
0
1
Cu 
Fr 
Sb 
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e 
0
1
4
2
e+
He +
0
1
e+
68
30
62
28
Zn
electron capture
Ni
positron
208
85
At
alpha particle
Te
beta particle
129
52
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Section 19.2
The Kinetics of Radioactive Decay
Rate of Decay
Rate = kN
 The rate of decay is proportional to the number of
nuclides. This represents a first-order process.
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Section 19.2
The Kinetics of Radioactive Decay
Half-Life
 Time required for the number of nuclides to reach half
the original value.
t1/ 2
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ln  2  0.693
=
=
k
k
16
Section 19.2
The Kinetics of Radioactive Decay
Nuclear Particles
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Section 19.2
The Kinetics of Radioactive Decay
Half-Life of Nuclear Decay
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Section 19.2
The Kinetics of Radioactive Decay
EXERCISE!
A first order reaction is 35% complete at the
end of 55 minutes. What is the value of k?
k = 7.8 × 10-3 min-1
Section 19.3
Nuclear Transformations
Nuclear Transformation
 The change of one element into another.
27
13
249
98
Al + He 
4
2
30
15
1
0
P+ n
263
Cf + 188 O  106
Sg + 4 01 n
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Section 19.3
Nuclear Transformations
A Schematic Diagram of a Cyclotron
21
Section 19.3
Nuclear Transformations
A Schematic Diagram of a Linear Accelerator
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Section 19.4
Detection and Uses of Radioactivity
Measuring Radioactivity Levels
 Geiger counter
 Scintillation counter
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Section 19.4
Detection and Uses of Radioactivity
Geiger Counter
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Section 19.4
Detection and Uses of Radioactivity
Carbon–14 Dating
 Used to date wood and cloth artifacts.
 Based on carbon–14 to carbon–12 ratio.
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Section 19.4
Detection and Uses of Radioactivity
Radiotracers
 Radioactive nuclides that are introduced into organisms
in food or drugs and whose pathways can be traced by
monitoring their radioactivity.
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Section 19.4
Detection and Uses of Radioactivity
Radiotracers
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Section 19.5
Thermodynamic Stability of the Nucleus
Energy and Mass
 When a system gains or loses energy it also gains or
loses a quantity of mass.
E = mc2
Δm = mass defect
ΔE = change in energy
 If ΔE is negative (exothermic), mass is lost from
the system.
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Section 19.5
Thermodynamic Stability of the Nucleus
Mass Defect (Δm)
 Calculating the mass defect for 42 He:

Since atomic masses include the masses of the electrons, we
must account for the electron mass.
4.0026 = mass of
1.0078 = mass of

4
2 He
1
1H
atom = mass of
atom = mass of
4
2 He
1
1H
nucleus + 2me
nucleus + me
He nucleus is “synthesized” from 2 protons and two
neutrons.
4
2
m =  4.0026  2me  
m =  0.0304 amu
2 1.0078  me  + 2 1.0087
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Section 19.5
Thermodynamic Stability of the Nucleus
Binding Energy
 The energy required to decompose the nucleus into its
components.
 Iron-56 is the most stable nucleus and has a binding
energy of 8.79 MeV.
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Section 19.5
Thermodynamic Stability of the Nucleus
Binding Energy per Nucleon vs. Mass Number
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Section 19.6
Nuclear Fission and Nuclear Fusion
Nuclear Fission and Fusion
 Fusion – Combining two light nuclei to form a heavier,
more stable nucleus.
 Fission – Splitting a heavy nucleus into two nuclei with
smaller mass numbers.
1
0
n+
235
92
U  142
56 Ba +
91
36
Kr + 3 01 n
 Bombardment+ Parent Daughters + neutrons
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Section 19.6
Nuclear Fission and Nuclear Fusion
Nuclear Fission
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Section 19.6
Nuclear Fission and Nuclear Fusion
Criterion for a self sustaining reaction:
 The target nuclei must produce at least one
neutrons upon splitting.
 The must be sufficient mass of target nuclei for
the reaction to continue.
 The mass defect must be sufficient in order to
produce high energy emissions.
Section 19.6
Nuclear Fission and Nuclear Fusion
Fission Processes
 A self-sustaining fission process is called a chain
reaction.
Neutrons
Causing
Fission
Event
Event
subcritical
<1
critical
=1
supercritical
>1
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Result
reaction stops
sustained reaction
violent explosion
35
Section 19.6
Nuclear Fission and Nuclear Fusion
Schematic Diagram of a Nuclear Power Plant
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Section 19.6
Nuclear Fission and Nuclear Fusion
Schematic Diagram
of a Reactor Core
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Section 19.6
Nuclear Fission and Nuclear Fusion
What does each part do?
 Fuel rods: Contains fissionable material
 Control Rods: Conic neutron “catchers” made of
boron or cadmium
 Heat exchanger: Web of pipes containing
superheated fluid that boils the water
 Reactor vessel: Contains reactor core
 Containment fluid: Fluid that surrounds
fissionable material also serves to control reaction
 Turbine: Spins when steam passes through
Section 19.6
Nuclear Fission and Nuclear Fusion
More parts
 Generator: Connected to turbine. Converts
mechanical Energy to electrical
 Condenser: Returns steam to water.
 External water source: Provides water for
condenser.
 Cooling tower: Releases excess heat so water can
be returned to ecosystem
 Pumps: Move fluid around and create elevated
pressure conditions
Section 19.4
Detection and Uses of Radioactivity
Nuclear Waste
High level
Low Level
Section 19.6
Nuclear Fission and Nuclear Fusion
Nuclear Energy?
Pros
Cons
Section 19.6
Nuclear Fission and Nuclear Fusion
Nuclear Fusion
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Section 19.7
Effects of Radiation
Biological Effects of Radiation
Depend on:
1.
2.
3.
4.
Energy of the radiation
Penetrating ability of the radiation
Ionizing ability of the radiation
Chemical properties of the radiation source
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Section 19.7
Effects of Radiation
rem (roentgen equivalent for man)

The energy dose of the radiation and its effectiveness in causing
biologic damage must be taken into account.
Number of rems = (number of rads) × RBE
rads = radiation absorbed dose
RBE = relative effectiveness of the
radiation in causing biologic damage
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Section 19.7
Effects of Radiation
Effects of Short-Term Exposures to Radiation
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