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Nuclear Chemistry
Chapter 18
AP Chemistry Nuclear
“Requirements”
•
•
•
•
•
Types of nuclear decay
Nuclear Stability
Half-life
Mass Defect and Binding Energy
Topic Appearance on Exam:
– 3/75 Questions
– Occasionally in FR
Radioactivity
Discovered by Antoine Henri Becquerel in 1896
– He saw that photographic plates developed bright spots
when exposed to uranium metals
The Experiment That Started it All
They were studying effect of
U- salts that were exposed to
sunlight and fogged
photographic film. On a
cloudy day, he left uranium
on the film and it made this
image.
Marie Curie and Antoine Becquerel-1896
Definitions
• Radioactivity - Process by
which substances give off
energy rays or particles.
• Radiation - What the actual
rays are called.
• Radioisotopes - Unstable
isotopes that become stable
by emitting energy and
radiation.
Marie Sklodowska Curie
Shared Physics Nobel Prize
1903 with her husband and
Becquerel for Radiation
Phenomenon
Chemistry Nobel Prize 1911
Discovery of Po and Ra.
Misunderstood Radiation
Misunderstood Radiation
The Radium Girls
Grace Fryer and the other women at the
radium factory in Orange, New Jersey, naturally
supposed that they were not being poisoned. It
was a little strange, Fryer said, that when she
blew her nose, her handkerchief glowed in the
dark. But everyone knew the stuff was harmless.
The women even painted their nails and their
teeth to surprise their boyfriends when the lights
went out. They all had a good laugh, then got
back to work, painting a glow-in-the-dark radium
compound on the dials of watches, clocks,
altimeters and other instruments.
Chemical vs. Nuclear Reactions
Chemical Reactions
Nuclear Reactions
Occur when bonds
are broken
Occur when nuclei
emit particles and/or
rays
Chemical vs. Nuclear Reactions
Chemical Reactions
Nuclear Reactions
Occur when bonds are broken
Occur when nuclei emit particles and/or
rays
Atoms remain
Atoms often
unchanged, although converted into atoms
they may be
of another element
rearranged
Chemical vs. Nuclear Reactions
Chemical Reactions
Nuclear Reactions
Occur when bonds are broken
Occur when nuclei emit particles and/or
rays
Atoms remain unchanged, although they
may be rearranged
Atoms often converted into atoms of
another element
Involve only valence May involve
electrons
protons, neutrons,
and electrons
Chemical vs. Nuclear Reactions
Chemical Reactions
Nuclear Reactions
Occur when bonds are broken
Occur when nuclei emit particles and/or
rays
Atoms remain unchanged, although they
may be rearranged
Atoms often converted into atoms of
another element
Involve only valence electrons
May involve protons, neutrons, and
electrons
Associated with
small energy
changes
Associated with
large energy changes
Chemical vs. Nuclear Reactions
Chemical Reactions
Nuclear Reactions
Occur when bonds are broken
Occur when nuclei emit particles and/or
rays
Atoms remain unchanged, although they
may be rearranged
Atoms often converted into atoms of
another element
Involve only valence electrons
May involve protons, neutrons, and
electrons
Associated with small energy changes
Associated with large energy changes
Reaction rate
influenced by
temperature, particle
size, concentration, etc.
Reaction rate is not
influenced by
temperature, particle
size, concentration, etc.
Review of Atomic Structure
Nucleus
Electrons
99.9% of the mass
1/10,000 the size of
the atom
0.01% of the mass
Review of Atomic Structure
Nucleus
Electrons
99.9% of the mass
1/10,000 the size of the atom
0.01% of the mass
Composed of
protons (p+) and
neutrons (n0)
Composed of
electrons (e-)
Review of Atomic Structure
Nucleus
Electrons
99.9% of the mass
1/10,000 the size of the atom
0.01% of the mass
Composed of protons (p+) and neutrons
(n0)
Composed of electrons (e-)
Positively charged
Negatively charged
Review of Atomic Structure
Nucleus
Electrons
99.9% of the mass
1/10,000 the size of the atom
0.01% of the mass
Composed of protons (p+) and neutrons
(n0)
Composed of electrons (e-)
Positively charged
Negatively charged
Strong nuclear force Weak electrostatic
(holds the nucleus
force (because they
together)
are charged
negatively
Three Main Types of Radiation
• Alpha
• Beta
• Gamma
Alpha Radiation
Loss of an -particle (a helium nucleus)
4
2
238
92
U
He
234

90
4
2
Th+ He
Alpha Radiation
Alpha radiation occurs when an unstable nucleus emits a
particle composed of 2 protons and 2 neutrons. The atom
giving up the alpha particle has its atomic number reduced
by two. Of course, this results in the atom becoming a
different element. For example, Rn undergoes alpha decay
to Po.
Beta Radiation
Beta Decay
Loss of a -particle (a high energy electron)

0
−1
1
0
n
131
53
I
or
0
−1
e
p
+

1
1

131
54
Xe
0
−1
+

0
−1
e
Beta Radiation
Beta radiation occurs when an unstable
nucleus emits an electron. As the emission
occurs, a neutron turns into a proton.
Gamma Radiation
Loss of a -ray (high-energy
radiation that almost always
accompanies the loss of a
nuclear particle)
0
0

Atomic number (Z) = number of protons in nucleus
Mass number (A) = number of protons + number of neutrons
= atomic number (Z) + number of neutrons
Mass Number
Atomic Number
A
ZX
Element Symbol
proton
1p
1H
or
1
1
neutron
1n
0
electron
0
0e
or
-1
-1
positron
0
0e
or
+1
+1
 particle
4He
4
or
2
2
A
1
1
0
0
4
Z
1
0
-1
+1
2
Penetrating Ability
Geiger-Müller Counter
Geiger Counter
• Used to detect radioactive substances
Balancing Nuclear Equations
1. Conserve mass number (A).
The sum of protons plus neutrons in the products must equal
the sum of protons plus neutrons in the reactants.
235
92 U
138
55 Cs
+ 10n
235 + 1
=
+
96
37 Rb
+ 2 10n
138 + 96 + (2 x 1)
2. Conserve atomic number (Z) or nuclear charge.
The sum of nuclear charges in the products must equal the
sum of nuclear charges in the reactants.
235
92 U
92
+ 10n
+ 0
138
55 Cs
+
96
37 Rb
+ 2 10n
= 55 + 37 + (2 x 0)
212Po
decays by alpha emission. Write the balanced
nuclear equation for the decay of 212Po.
alpha particle - 42He or 42
212Po
84
4He
2
+ AZX
212 = 4 + A
A = 208
84 = 2 + Z
Z = 82
212Po
84
4He
2
+ 208
82Pb
Nuclear Stability and Radioactive Decay
Beta decay
+-10 + n
14C
6
14N
7
40K
19
40Ca
20
Decrease # of neutrons by 1
+ -10 + n
1n
0
Increase # of protons by 1
1p
1
+ -10 + n
Positron decay
++10 + n
Increase # of neutrons by 1
++10 + n
Decrease # of protons by 1
11C
6
11B
5
38K
19
38Ar
18
1p
1
1n
0
++10 + n
n and n have A = 0 and Z = 0
Nuclear Stability and Radioactive Decay
Electron capture decay
+n
37Ar
18
+ -10e
37Cl
17
55Fe
26
+ -10e
55Mn
25
1p
1
Increase # of neutrons by 1
+n
Decrease # of protons by 1
+ -10e
1n
0
+n
Alpha decay
212Po
84
4He
2
+ 208
82Pb
Spontaneous fission
252Cf
98
1n
2125
In
+
2
49
0
Decrease # of neutrons by 2
Decrease # of protons by 2
Learning Check
What radioactive isotope is produced in the
following bombardment of boron?
10B
5
+ 4He
2
? +
1n
0
Learning Check
What radioactive isotope is produced in the
following bombardment of boron?
10B
5
+ 4He
2
13N
7
+
1n
0
Write Nuclear Equations!
Write the nuclear equation for the beta
emitter Co-60.
60Co
0e
27
-1
+
60Ni
28
Artificial Nuclear Reactions:
Transmutation
New elements or new isotopes of known elements
are produced by bombarding an atom with a
subatomic particle such as a proton or neutron -or even a much heavier particle such as 4He and
11B.
Reactions using neutrons are called  reactions
because a  ray is usually emitted.
Radioisotopes used in medicine are often made by
 reactions.
Artificial Nuclear Reactions
Example of a 
reaction is production
of radioactive 31P for use in studies of P
uptake in the body.
31 P
15
+
1 n
0
--->
32 P
15
+ 
Transuranium Elements
Elements beyond 92 (transuranium) made
starting with an  reaction
238 U
92
+
239 U
92
239 Np
93
1
0n --->
239 U
92
+ 
--->
239 Np
93
+ 0-1
--->
239 Pu
94
+
0
-1
Nuclear Stability
•
Certain numbers of neutrons and protons are extra stable
•
n or p = 2, 8, 20, 50, 82 and 126
•
Similar to extra stable numbers of electrons in noble
gases (e- = 2, 10, 18, 36, 54 and 86)
•
Nuclei with even numbers of both protons and neutrons
are more stable than those with odd numbers of neutron
and protons
•
All isotopes of the elements with atomic numbers higher
than 83 are radioactive
•
All isotopes of Tc and Pm are radioactive
23.2
Zone of Stability
and Radioactive
Decay
Radioisotopes
lying outside the
zone will undergo
spontaneous
decay until
located within the
zone!
Half-Life (Kinetics)
• HALF-LIFE is the time that it takes for
1/2 a sample to decompose.
• The rate of a nuclear transformation
depends only on the “reactant”
concentration.
Half-Life
Decay of 20.0 mg of 15O. What remains after 3 halflives? After 5 half-lives?
Kinetics of Radioactive Decay
For each duration (half-life), one half of the
substance decomposes.
For example: Ra-234 has a half-life of 3.6 days
If you start with 50 grams of Ra-234
After 3.6 days > 25 grams
After 7.2 days > 12.5
grams
After 10.8 days > 6.25
grams
Kinetics of Radioactive Decay
A
daughter
DA
rate = Dt
A = A0e(-kt)
lnA = lnA0 - kt
A = the amount of atoms at time t
A0 = the amount of atoms at time t = 0
k is the decay constant (sometimes called l)
t½ = Ln 2
k
0.693
t½ =
k
Carbon Dating (no…not for Prom)
In case you missed the boat…
Carbon-14
Cycle
t1/2 for 14C is
5730 years
Our recent trip to LA for WOF…a side trip to the La
Brea Tar Pits!
Radio Carbon Dating
Iceman Ötzi
• On 19 September 1991 an extraordinary
archaeological discovery was made at a
high-altitude mountain pass of the Ötztal
Alps near the Austrian-Italian border.
• Two alpine mountaineers discovered a body
partially frozen in a melting glacier.
Iceman Ötzi
Iceman Ötzi
14C
dating of the Iceman
• Accelerator mass spectrometry (AMS)
measurements of 14C in bone and tissue of
the Iceman Ötzi revealed that the
approximate date of death was 4550 years
ago.
• The carbon-14 in living tissue has a
disintegration rate of 13.6 counts per
minute.
Learning Check!
Determine the counts per minute of the 14C in
the tissue of the iceman based on the
approximate age of this specimen.
7.84 counts per minute
Radiocarbon Dating – Carbon-14 and Uranium-238
14N
7
+ 01n
14C
6
14C
6
14N
7
+ 11H
+ -10 + n
t½ = 5,730 years
Uranium-238 Dating
238U
92
206Pb
82
+ 8 24 + 6-10
t½ = 4.51 x 109 years
14-step decay
process here!
Learning Check!
1) The half life of I-123 is 13 hr.
How much
of a 64 mg sample of I-123 is left after 31
hours?
2) #31 on p. 870
Biological Effects of Radiation
Radiation absorbed dose (rad)
1 rad = 1 x 10-5 J/g of material
Roentgen equivalent for man (rem)
1 rem = 1 rad x Q
Quality Factor
-ray = 1
=1
 = 20
Effects of Radiation
Nuclear Radiation
Avoidable Radiation!
Brain-free zones
If you fail to avoid the
radiation risk…
Nuclear Fission
Fission involves the “splitting” of atoms with a very
large nucleus. Typically, these are generally not as stable.
Fission chain has three general steps:
1. Initiation. Reaction of a single atom starts the
chain (e.g., 235U + neutron)
2. Propagation.
235U
fission releases neutrons that
initiate other fissions
3. Termination. Fissile material is exhausted.
Nuclear Fission
Representation of a fission process.
Mass Defect
• Some of the mass can be converted into
energy
• Shown by a very famous equation!
E=mc2
Energy
Mass
Speed of light
Nuclear Fission
235U
92
+ 01n
90Sr
38
1n + Energy
+ 143
Xe
+
3
0
54
Energy = [mass 235U + mass n – (mass 90Sr + mass 143Xe + 3 x mass n )] x c2
Energy = 3.3 x 10-11J per 235U
= 2.0 x 1013 J per mole 235U
Combustion of 1 ton of coal = 5 x 107 J
Nuclear binding energy (BE) is the energy required to break
up a nucleus into its component protons and neutrons.
BE + 199F
911p + 1010n
E = mc2
BE = 9 x (p mass) + 10 x (n mass) – 19F mass
BE (amu) = 9 x 1.007825 + 10 x 1.008665 – 18.9984
BE = 0.1587 amu
BE = 2.37 x 10-11J
1 amu = 1.49 x 10-10 J
Converts amu to kg and multiplies by c2
binding energy
binding energy per nucleon =
number of nucleons
2.37 x 10-11 J
= 1.25 x 10-12 J
=
19 nucleons
Nuclear binding energy per nucleon vs Mass number
This is the energy
transition for fission!
nuclear binding energy
nucleon
nuclear stability
Nuclear Fission
Nuclear chain reaction is a self-sustaining sequence of
nuclear fission reactions.
The minimum mass of fissionable material required to
generate a self-sustaining nuclear chain reaction is the
critical mass.
Non-critical
Critical
Nuclear Fission Weapons
Trinity Site explosion, 0.016 second after
explosion, July 16, 1945. Note that the viewed
hemisphere's highest point in this image is about 200 meters
high
Nuclear Fission Weapons
Nuclear Fission Weapons
Nuclear Fission Weapons
Nuclear Fission & POWER
• Currently about 103
nuclear power plants in the
U.S. and about 435
worldwide. (another 71
under construction)
• 17% of the world’s energy
comes from nuclear.
Diagram of a nuclear power plant
The
Core of
a
Reactor
Nuclear Fission
Annual Waste Production
35,000 tons SO2
4.5 x 106 tons CO2
3.5 x 106
ft3 ash
1,000 MW coal-fired
power plant
70 ft3
vitrified
waste
1,000 MW nuclear
power plant
Nuclear “Accidents”
Three Mile Island – partial meltdown
due to lost coolant
Chernobyl – Fault of operators and
testing safety equipment
too close to the limit.
France – safe operation provides
2/3 of power requirements for the
country.
Chernobyl
Chernobyl
Chernobyl
Chernobyl
Chernobyl
Chernobyl
http://www.youtube.com/watch?
v=t7Jfx2kEi_k
Seconds From Disaster : Meltdown at Chernobyl
- FULL
Most Recent Nuclear Disaster
Nuclear Fusion
Fusion
small nuclei combine
2H
1
+
3H
4He
1
2
+ 1n +
0
Occurs in the sun and other stars
Energy
Nuclear Fusion
Fusion – Overcoming electrostatic
repulsion…
• Excessive heat is difficult to contain
• Attempts at “cold” fusion have
FAILED.
• “Hot” fusion is currently under
intense study!
Fusion
Fusion Basics
Inertial Confinement Fusion
Tokamak Fusion Reactor
Slightly Uncontrolled Fusion
How do we get uncontrolled fusion?
VERY CAREFULLY!!!
Nuclear binding energy per nucleon vs Mass number
Now we are interested
in this transition for
fusion!
nuclear binding energy
nucleon
nuclear stability
Other Military Uses of Uranium
Depleted Uranium – the
fissionable U-235 extracted
Due to the high density of U-238
(almost equal to Au or W)
•Armor Plating
•Armor Penetrators
•Special ability of uranium to be
self-sharpening and
pyrophoric…both desirable for
killing armor and its crew.
Radioisotopes in Medicine
•
1 out of every 3 hospital patients will undergo a nuclear
medicine procedure
•
24Na,
•
131I,
t½ = 14.8 hr,  emitter, thyroid gland activity
•
123I,
t½ = 13.3 hr, -ray emitter, brain imaging
•
18F,
t½ = 1.8 hr,  + emitter, positron emission tomography
•
99m Tc,
t½ = 14.8 hr,  emitter, blood-flow tracer
t½ = 6 hr, -ray emitter, imaging agent
Brain images
with 123I-labeled
compound
Chemistry In Action: Food Irradiation
Dosage
Effect
Up to 100 kilorad
Inhibits sprouting of potatoes, onions, garlics.
Inactivates trichinae in pork. Kills or prevents insects
from reproducing in grains, fruits, and vegetables.
100 – 1000 kilorads
Delays spoilage of meat poultry and fish. Reduces
salmonella. Extends shelf life of some fruit.
1000 to 10,000 kilorads
Sterilizes meat, poultry and fish. Kills insects and
microorganisms in spices and seasoning.