Nuclear Chemistry
Nine Mile
Oswego, NY
 Radioisotope – an isotope that is
radioactive
 Example: Carbon-14
 Radioactive isotopes can be naturally
occurring, or they can be produced by
bombarding stable isotopes with high
speed particles
Stability
 All nuclei with atomic numbers greater
than 83 are unstable
 They are all radioactive
 Stability is also dependant upon the ratio
of protons to neutrons
 The closer an isotope is to a 1:1 ratio the
more stable it is
Transmutation


Any change in the nucleus, which causes
the element to change into a new element
(change of atomic number)
Can occur naturally or artifically
Natural Transmutation


Occurs naturally
Single nucleus undergoes decay
Example: 3719K → 3718Ar + 0+1e
Artificial Transmutation


If the change is brought about by
bombarding the nuclei by high energy
particles
Two reactants – a fast moving particle and
the target material
Example: 3216S + 10n→ 3215P + 11H
Equations


Mass must be conserved
Atomic mass and atomic number must be
the same on both sides of the equation
Remember
 42He


4 = superscript = mass number (atomic mass) =
protons + neutrons
2 = subscript = atomic number = protons
Equation Examples
1.
What is X?
6 Li
3
2.
+ 10n → 42He + X
What is X?
14 C
6
→ X + 0-1e
Types of Radiation – Table O




Alpha particles – helium nucleus, 2
protons, 2 neutrons
Beta particles – an electron,
negative charge, no mass
Positron – electron with a positive
charge, no mass
Gamma radiation (γ) – similar, but
more energy than X-rays, no mass,
no charge
Particle Mass Charge
(amu)
Symbol
Penetrating
Power
Shielding
Alpha
4
+2
α, 42He
Low
Paper,
clothing
Beta
0
-1
β-, 0-1e
Moderate
Metal foil
Positron
0
+1
β+, 0+1e
Moderate
Metal foil
Gamma
0
0
γ
High
Lead,
concrete
Charges of Decay Particles
•Negative particles will be attracted to positive charges
•Positive charges will be attracted to negative charges
•Non charged particles are not affected by charges



Alpha Decay – unstable nucleus emits an
alpha particle
Example: 22688Ra → 22286Rn + 42He
Beta Decay – unstable nucleus emits a
beta particle
Example: 21482Pb → 21483Bi + 0-1e
Positron Emission – unstable nucleus
emits a positron
Example: 3719K → 3718Ar + 0+1e
Conversion of Mass to Energy
E = mc2
– E = energy (J)
– m = mass (kg)
– c = velocity (speed) of light = 3.0x108m/s
Example: How many joules of energy are
released if 1.0g is converted to energy?
Mass Defect
The actual atomic mass of an atom is less
than what we would predict based upon
the mass of individual protons and
neutrons
The difference is because energy is
released when the protons and neutrons
combine
The larger the mass defect, the more
energy is released upon formation, and
the more stable the particle is
Examples
1. Calculate the predicted mass of He-4.
1 proton = 1.00728, 1 neutron = 1.00867
•
The actual mass of He-4 = 4.00150
•
The mass defect is =
2. Convert the mass defect to energy (using E =
mc2)
Fission
 Splitting of a heavy nucleus to produce lighter
nuclei
 Nuclear Power Plants
 Neutron joins with a nucleus of a heavy
element
 Intermediate product is very unstable
 Splits apart producing
 Two mid weight nuclei
 At least one neutron
 A great amount of energy
Fission
• Example:
235 U
92
+
1 n
0
 9236Kr +
141 Ba
56
+ 3
1 n
0
+ energy
• The three neutrons given off can be
reabsorbed by other U-235 nuclei to continue
fission as a chain reaction
• A tiny bit of mass is lost (mass defect) and
converted into a huge amount of energy
• See Fission
Chain Reaction


The neutrons that are emitted can become
reactants causing more nuclei to undergo
fission and release more energy
The reaction can be controlled by limiting the
number of interactions between neutrons and
nuclei
Nuclear Power Plants
Main Components



Fuel – Uranium or Plutonium
Control Rods - absorb neutrons to control the rate
of the reaction
Containment Structure – building that houses the
reactor
Main Components


Coolant – Water, cools
the reaction
Cooling Tower – cools
the discharge water,
releases water vapor
Nuclear Power

Advantages:



Cleaner than conventional fossil fuels – no
greenhouse gases or acid rain
More efficient, cleaner
Disadvantages:

Many of the bi-products of the reactions are
radioactive (unstable) and have long half-lives,
making the storage and disposal of these wastes
dangerous
Fusion
 Combining of light nuclei
to produce a heavier nucleus
 The Sun, Hydrogen Bomb
Example: 21H + 21H → 42He + energy
 See Fusion
Fusion
 Advantages
 Products are not highly radioactive
 Produces a lot of energy
 Disadvantages
 Requires extremely high temperatures and
pressures, therefore not yet available to
produce energy on Earth
Half-Life
 Time it takes for half of the atoms in a given
sample of an isotope to decay
 Each isotope has its own half-life (Table N)
 The shorter the half-life of an isotope, the less
stable it is
 Half-life is a constant factor, it is not affected
by temperature or pressure
 Geiger counter can be used to record the
decay of an isotope
•Use Table N for HalfLife and Decay Modes
1. Calculate the mass of I-131 that
remains after 32.28 days, if the
mass of the original sample was
100.0g.
2. If 50.0g of a radioactive isotope
decays to 6.25g in 60.0 days, what
is the isotope’s half-life?
3.
4.
5.
What fraction of a phosphorus-32
sample will remain after 28.6 days?
50.0g of cobalt-60 decays for 21
years. How many grams remain
after this time?
After 14.4 seconds, 3.00g of
nitrogen-16 remains. What was the
mass of the original nitrogen-16
sample?
Dating
Each radioactive substance is presently
decaying at the same rate as when the
substance
 By comparing the amount of 14C that
remains to the amount of 12C that is
present, the amount of 14C (and the age)
can be calculated

Chemical Tracers
A radioisotope is used to follow the path of
a chemical process
Example: C-14 is used to follow the path of
carbon in organic reactions

Medical Applications
• Some radioisotopes have the ability to kill
living tissue
• Any radioisotope used in medicine
must have a short half-life, making it
quickly eliminated by the body
Medical Examples
• Cancer: Cobalt-60 emits large amounts of
gamma radiation which can be used to kill
tumor cells
• Thyroid: Iodine-131 is used in the detection
and treatment of thyroid conditions
• Gamma Radiation: meats are irradiated to kill
bacteria, producing a longer shelf life
• Anthrax: Cobalt-60 and Cesium-137 are two
sources of gamma radiation that can be used
to destroy anthrax
Radiation Risks



Can damage normal cells
High doses can cause illness, death
Can cause mutations that can be passed onto
offspring