# Nuclear Chemistry

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```					Nuclear Chemistry
Chapter 21
Nuclear Reactions

Some nuclei are unstable. They are said
to be radioactive and emit particles and
usually high-energy electromagnetic
radiation (gamma rays) at the same time.

Other nuclear reactions involve
bombarding nuclei with particles such as
neutrons, protons, alpha particles or other
nuclei. (particle accelerators)
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      A
ZX
Element Symbol
Atomic Number

proton    neutron     electron      positron        a particle
1p
1   or 1H
1
1n
0
0e
-1  or -1b
0      0e
+1  or +1 b
0       4He
2    or 4a
2

A         1          1            0             0               4

Z         1          0           -1             +1              2

23.1
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               138          96
92 U   + 1n
0        55 Cs   +   37 Rb   + 2 1n
0

235 + 1 = 138 + 96 + 2x1

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               138          96
92 U   + 1n
0        55 Cs   +   37 Rb   + 2 1n
0

92 + 0 = 55 + 37 + 2x0
23.1
212Podecays by alpha emission. Write the balanced
nuclear equation for the decay of 212Po.

alpha particle - 4He or 2a
4
2

212Po       4He   + AX
84         2       Z

212 = 4 + A         A = 208

84 = 2 + Z          Z = 82

212Po      4He   + 208Pb
84        2        82

23.1
23.1

Beta decay
14C
6
14N
7
+-1 b + n
0
Decrease # of neutrons by 1
40K
19
40Ca
20
+ -1b + n
0
Increase # of protons by 1
1n
0
1p
1
+ -1b + n
0

Positron decay
11C
6
11B
5
++1b + n
0
Increase # of neutrons by 1
38
19K
38Ar
18
++1b + n
0
Decrease # of protons by 1
1p
1
1n
0
++1b + n
0

n and n have A = 0 and Z = 0
23.2
Electron capture decay
37Ar
18
0
+ -1e       37Cl
17
+n        Increase # of neutrons by 1
55Fe
26
0
+ -1e       55Mn
25
+n      Decrease # of protons by 1
1p
1
0
+ -1e   1n
0
+n
Alpha decay

Decrease # of neutrons by 2
212Po           4He   + 208Pb
84             2        82
Decrease # of protons by 2

Spontaneous fission

252Cf           2125In + 21n
98               49      0
23.2
Example 21.1

Write balanced nuclear equations for the

a. Decay of U-238 to Th-234
b. Decay of Cs-137 to Ba-137
c. Emission of a beta particle by As-78
n/p too large
beta decay

X

Y

n/p too small
positron decay or electron capture

23.2
Nuclear Stability
•   Certain numbers of neutrons and protons are extra stable
•   n or p = 2, 8, 20, 50, 82 and 126
•   Like 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
•   All isotopes of Tc and Pm are radioactive

23.2
Nuclear binding energy (BE) is the energy required to break
up a nucleus into its component protons and neutrons.
BE + 19F
9        91p + 101n
1      0

Δ E = (Δ m)c2
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          1 amu = 1.49 x 10-10 J
BE = 2.37 x 10-11J

binding energy
binding energy per nucleon =
number of nucleons
2.37 x 10-11 J
=                = 1.25 x 10-12 J
19 nucleons
23.2
Nuclear binding energy per nucleon vs Mass number

nuclear binding energy
nuclear stability
nucleon
23.2
Ex 21.2 The atomic mass of I-127 is
126.9004 amu. Calculate the nuclear
binding energy and the BE per nucleon.

c = 3.00 x 108m/s
1 kg = 6.02 x 1026 amu
1 J = 1 kg m2/s2

Nuclei outside the belt of stability or
with more than 83 protons are
unstable and decay naturally.

This decay obeys 1st order kinetics
and therefore has a constant half-life.
N         daughter
DN
rate = -          rate = lN
Dt
DN
-    = lN
Dt
N = N0exp(-lt)      lnN = lnN0 - lt
N = the number of atoms at time t

N0 = the number of atoms at time t = 0

l is the decay constant

ln2
l =
t½
23.3

[N] = [N]0exp(-lt)               ln[N] = ln[N]0 - lt

ln [N]
[N]

23.3
EH Assignment
Unit 23                              Mininum score
Sec 1 Properties of Radiation        90
Sec 2 Balancing Nuclear Reactions    90
Sec 3 Predicting Nuclear Stability   90
Sec 4 Radiation Decay Kinetics       90
Sec 6 Nuclear Binding Energy         90

Final Exam – June 17
14N     1
+ 0n         14C   + 1H
7                  6      1

14C
6
14N
7
+ -1b + n
0
t½ = 5730 years

The C-14 isotope is produced in the upper
atmosphere N-14 through the action of cosmic
rays. All living organisms contain C-14, but
when the organism dies the amount of C-14
decreases.

Paper from the Dead Sea Scrolls was found to
have only 0.795 times as much C-14 as that of a
living plant. What is the age of the scroll?

23.3
Age of Rocks
K-40 decays to Ar-40 with a half life of
1.2 x 109 years.
Uranium-238 Dating
238U
92
206Pb
82     + 8 2 a + 6-1 b
4       0
t½ = 4.51 x 109 years

23.3
Nuclear Transmutations

In 1919 Rutherford bombarded N with
alpha particles and produced O-17. This
was the first manmade nuclear reaction.

Why not just mix N and He?

Example 21.3

Neutrons are particularly useful in
producing synthetic isotopes since they
have no charge.
Nuclear Transmutation

14N
7      + 2a
4    17O
8
+ 1p
1

27
13 Al   + 2a
4    30P
15
1
+ 0n

14N
7
1
+ 1p   11C
6
+ 4a
2

Cyclotron Particle Accelerator

23.4
Nuclear Transmutation

23.4
A new type of nuclear reaction – fission-
was discovered in 1938. The experiments
were carried out in Germany by Hahn and
Strassman and interpreted by Lisa
Meitner.

U-235 and Pu-239 will undergo fission
when bombarded with neutrons.

U-235 makes up 0.7% of natural uranium
and Pu-239 can be produced from the
more abundant U-238.
Nuclear Fission

235U     1
+ 0n       90Sr   + 143Xe + 31n + Energy
92               38        54      0

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
23.5
Nuclear Fission
Representative fission reaction
235U     1
+ 0n     90Sr   + 143Xe + 31n + Energy
92             38        54      0

23.5
Notice that the fission products
are not the normal isotopes and
This is true of fission bombs and
nuclear reactors.
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
23.5
The little boy bomb. It used U-235
The fat man bomb. It used Pu-239
Fig. 21.9
Nuclear Fission

Schematic
diagram of a
nuclear
fission reactor

Much of the heat comes
from decay of fission
products. Even if
fission stops, this
decay does not.

23.5
Nuclear Fission

35,000 tons SO2               Annual Waste Production
4.5 x 106 tons CO2

70 ft3
3.5 x 106                   vitrified
ft3 ash                     waste

1,000 MW coal-fired                1,000 MW nuclear
power plant                       power plant
23.5
Nuclear Fission

Hazards of the
fuel compared to
uranium ore

From “Science, Society and America’s Nuclear Waste,” DOE/RW-0361 TG   23.5
Nuclear Fusion

Fusion Reaction             Energy Released
2     2      3     1
1 H + 1H     1 H + 1H            6.3 x 10-13 J
2H
1
3
+ 1H      4He
2     + 1n
0
2.8 x 10-12 J
6Li     2
+ 1H     2   4He           3.6 x 10-12 J
3                  2

High T required.
Why?

Tokamak magnetic
plasma
confinement

23.6
Thermonuclear
bombs

Mark 17 model
•   1 out of every 3 hospital patients will undergo a nuclear
medicine procedure
•   24Na,    t½ = 14.8 hr, b emitter, blood-flow tracer
•   131I,   t½ = 14.8 hr, b emitter, thyroid gland activity
•   123I,   t½ = 13.3 hr, g-ray emitter, brain imaging
•   18F,    t½ = 1.8 hr, b+ emitter, positron emission tomography
•   99mTc,    t½ = 6 hr, g-ray emitter, imaging agent

Brain images
with 123I-labeled
compound

23.6
Geiger-Müller Counter

23.6
1 rad = 1 x 10-5 J/g of material
Roentgen equivalent for man (rem)
1 rem = 1 rad x Q    Quality Factor
g-ray = 1
b=1
a = 20

23.6
The Standard Model is the name
give to the current theory of
fundamental particles and how they
interact.
There are four fundamental forces in
nature.

1. Electromagnetic force
2. Gravity
3. Strong nuclear force
4. Weak nuclear force
Electroweak Theory has shown that 1 and 4 are really
different aspects of the same force.
There are 12 fundamental fermion
particles in nature. (spin =1/2, 3/2,
5/2, …

6 flavors of quarks and 6 flavors of
leptons. All the matter that we are
familiar with are made up of two
quarks – up and down and one
lepton – the electron.
The other category of particles are
the bosons (spin =0, 1, 2,…)

The bosons are force carriers. For
example, the electromagnetic
force is caused by an exchange of
photons.

Each force has one or more force
carriers.
The strong nuclear force is carried
by gluons. Quarks come in three
colors – red, green and blue. This
is analogous to + and – for the
electromagnetic force.

Unlike colors attract. This force is
also called the color force.
Fermilab

Ring is 4 miles around.
Protons and antiprotons
collide.
Fermilab – particle tracks in detector.
Discovery of top quark.
and Ca-45, c. Mo-95, Tc-92 d. Hg-195, Hg-196

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 views: 4 posted: 8/9/2012 language: pages: 50