Transcript NUCLEAR

NUCLEAR CHEMISTRY
I. Unlike other chemical reactions that
involve the transfer of electrons, nuclear
reactions involve changes in the
nucleus
II. Transmutations- When the atomic
nucleus of one element is changed
into a different element.
III. Why are certain elements or isotopes
radioactive?
A. Their nuclei are unstable
B. Nuclei become unstable when the
ratio of neutrons to protons becomes
greater than 1.5 (approximately)
C. All elements with an atomic number
greater than 83 are radioactive and all
their isotopes
D. Elements with atomic numbers less
than 83 have some isotopes that are
radioactive and some that are stable.
IV. Unstable Nuclei Spontaneously decay to
Produce Stable nuclei by:
Alpha Decay-When an unstable nucleus
emits an alpha particle
1. Table O
2. alpha particle is a helium nucleus
3. Symbol: 42He or α
4. Example
226 Ra --- 222 Rn + 4 He
88
86
2
B. Beta Decay- when an unstable nucleus
emits a beta particle.
1. Table O
2. Beta particle is an electron
3. Symbol:
4. Example: 23490 Th-- 23491 Pa + 0-1 e
C. Positron Emission- When an unstable
nucleus emits a positron
1. Table O
2. Positron is a positive electron
3. Symbol: 0+1e orβ+
4. Example:
37 K  37 Ar + 0 e
19
18
+1
D.Gamma Radiation
1. Table O
2. Similar to high energy x-rays
Not particles and do not have mass
3. Symbol: ɤ
E. Table N shows types of decay
(transmutations) exhibited by various
nuclei
V. Nuclear Equations
A. Balancing
1. Both mass and charge are conserved
2. The top number means mass
3. The bottom number means charge
4. The sum of the upper numbers (mass) on each
side and the lower numbers (charge) on each side
must be equal.
5. Example
+ 10n  2411Na + X
Top = 28
Top = 24 so x must have a
mass of 4
Bottom = 13 Bottom = 11 so X must have
charge of +2
Use the periodic table or table O to identify
X it is 42He
27 Al
13
VI. Transmutations
A. Natural- When an unstable nuclei
spontaneously emits an alpha particle,
gamma ray, beta particle or positron.
1. All natural transmutations have only
one reactant
2. Example: 23994 Pu 23592U + 42He
B. Artificial- When a nucleus is bombarded
with high energy particles which brings
about a change in the nucleus.
1. Two types
a. Collision of a charged particle with
the nucleus
aa. The charged particle is accelerated
to a high speed in a device called a
cyclotron or synchrotron. These devices
use electric and/or magnetic fields to
speed up a charged particle so it can enter
the nucleus
bb. Example
32 P + 0 e  32 Si
15
-1
14
•
b. Collisions of neutrons with a nucleus
aa. The neutron is captured by the strong
force that holds protons and neutrons in
the nucleus.
bb. Example
238
1 n  239 U
U
+
92
0
92
c. To tell the difference between artificial
and natural transmutations look at the left
side of the equation. Natural
transmutations have a single nucleus on
the left and artificial transmutations have
two reactants.
VII. SEPARATING EMANATIONS
1. Done by using electric and magnetic
fields
2. In an electric field, alpha particles are
deflected toward the negative electrode,
beta particles are deflected toward the
positive electrode and gamma rays are
unaffected.
VIII. Fission and Fusion
A. Fission- The splitting of a heavy
nucleus to produce lighter nuclei by
capturing a neutron
1. Product of fission are two middle
weight nuclei, one or more neutrons, and
energy
2. Products are highly radioactive
3. This is the type of nuclear reaction
used in power plants
4. Example:
1 n +235 U 142 Ba +91 Kr+31 n +
0
92
56
36
0
energy
B. Fussion- Combining of light nuclei to
form heavier one
1. This is the process that occurs on the
sun
2. The light elements are generally
hydrogen or helium
3. Require extremely high temperatures
4. Products are not radioactive
5. Example: 1 H + 1 H  2 H + 0 e
IX. HALF-LIFE
A. Definition- Time required for one half of
the nuclei in a given sample to decay
B. The shorter the half-life the less stable
the nucleus
C. Table N
Example: What mass of I-131 remains after
32 days if you start with 100g.
To solve set up a table
number of ½ lives
time
amount (g)
• 0
0
100g
• 1 ½ life
8 days
50g
• 2 ½ lives
16 days
25 g
• 3 ½ lives
24 days
12.5 g
• 4 ½ lives
32 days
6.25 g
Examples: Analysis of a charred piece of
coal reveals it contains ¼ of the C-14 that
is found in living tissue.
Assume you started with 1gram
# ½ lives
Time
amount (g)
0 ½ lives
0
1
1 ½ life
5,770y
½
2 ½ lives
11,540 y
¼
X. Uses of Radioisotopes
A. Dating
1. C-14 is used to date once living
organisms
2. U-238 decays into Pb-206 and the
ratio of U-238/Pb-206 is used to date
rocks and other geological formations
B. Chemical Tracers – a radioactive
substance is used to follow the path of a
material within a system
1. P-31 Present in fertilizers and is used to
follow plant process
2.
C-14 can be used to follow metabolic
processes
C. Industrial applications
1. Gamma rays can be used to
measure the thickness of materials or
test the strength of a weld. The more
gamma rays a substance absorbs the
thicker it is.
D. Medical Applications- Certain
radioisotopes that are quickly eliminated
from the body and have short half-lives
are important as tracers in medical
diagnosis.
1. I-131 used to diagnose thyroid
disorders
2. Cobalt-60 emits large amounts of
gamma arrays and can be aimed at
tumors to kill cancerous cells
3. Technetium-99 is rapidly absorbed by
cancer cells. It is given to patients so
tumors can be detected in scans,
4. Co-60 and Cs-137 are sources of
gamma rays used to kill anthrax
5. Intense beams of gamma radiation
can be used to irradiate foods to kill
bacteria.
XI. Risks of Radiation
1. Exposure to high doses of radiation
can cause radiation sickness, cancer
and mutation in cells.
2. The by-products of nuclear power
plants, spent fuel rods and equipment, are
highly radioactive with long half-lives
and must be stored for many years.
3. Safety issues associated with
nuclear power plants. Chernobyl in the
Ukraine, 3 mile island in US.