Transcript Nuclear Chemistry

Nuclear
Chemistry
Only one element has unique names
for its isotopes …
1
1H
 hydrogen
2
H
1
 deuterium
3
H
1
 tritium
Deuterium and tritium are used in
nuclear reactors and fusion research.
Some isotopes are radioactive
Radioactive isotopes are called
radioisotopes.
Radioisotopes can emit alpha,
beta or gamma radiation as
they decay.
Man-made Isotopes
Man-made isotopes are usually
made by bombarding atoms with
protons or neutrons.
Cobalt-59 occurs naturally. When a
neutron “sticks” to the nucleus,
cobalt-60 is formed.
Uses for Isotopes
Radioisotopes are used to kill cancer
cells. (Co-60, Bi-212)
Radioisotopes are used in “imaging”
living and nonliving systems.
Radioisotopes are used as tracers
in chemical reactions.
Properties of alpha,
beta and gamma
radiation
Subatomic particles
1
0
proton
1
1
H
n
neutron
electron
e
-1
0
What do the numbers represent?
Mass number /Atomic number
Mass number
Protons in
nucleus
U
92
Atomic number
235
protons
+ neutrons
Mass number
Symbol of
Element
Alpha (a) particles are the
nuclei of helium atoms
4
and have the symbol 2He .
What is the
atomic number
of an a particle?
2
4
He
Alpha (a) particles are the
nuclei of helium atoms
4
and have the symbol 2He .
How many times heavier
is an alpha particle than
a hydrogen atom?
4
Beta (b) particles are high
speed electrons ejected from
the nuclei of atoms and have
0
the symbol -1e .
What is the
mass number of
a b particle?
-1
0
e
Beta (b) particles are high
speed electrons ejected from
the nuclei of atoms and have
0
the symbol -1e .
No protons or
neutrons in an
electron.
-1
0
e
Beta (b) particles are high
speed electrons ejected from
the nuclei of atoms and have
0
the symbol -1e .
What is the difference
between a b particle and None
a “regular” electron?
Beta (b) particles are high
speed electrons ejected from
the nuclei of atoms and have
0
the symbol -1e .
What is the difference Location
between a b particle and Location
Location
a “regular” electron?
Gamma (g) rays are high
energy electromagnetic
waves, not particles.
No protons, neutrons or electrons.
Gamma rays have short wavelengths
and high energies and travel at the
speed of light.
Gamma rays have short wavelengths
Increasing energy
… and high energies.
Alpha, Beta, Gamma
Electric field from electrically charged plates
+ + + + + + + +
What is the effect of an electric
field on a, b, g ?
- - - - - - - - Radioactive Source
Alpha, Beta, Gamma
Electric field from electrically charged plates
+ + + + + + + +
b
- - - - - - - - -
g
a
Radioactive Source
Alpha, Beta, Gamma
Electric field from electrically charged plates
b
Are a, b and g rays deflected
g
by magnetic fields?
- - - - - - - - a
+ + + + + + + +
Radioactive Source
Alpha, Beta, Gamma
Paper
Lead
a
Radioactive
Source
Aluminum
foil
Alpha, Beta, Gamma
Paper
Lead
b
a
Radioactive
Source
Aluminum
foil
Alpha, Beta, Gamma
Paper
Lead
b
a
Radioactive
Source
Aluminum
foil
g
Radiation Project
Create a table listing
information for each of the
three kinds of radiation:
Alpha, beta and gamma
Properties to include in your table:
(1)
(2)
(3)
(4)
(5)
Greek letter (6) relative mass
symbol
(7) relative. charge
actually is
(8) penetrating
atomic number ability
mass number (9) shielding
Nuclear Properties Table
Property
Alpha
Beta
Gamma
Greek Letter
Symbol
Actually is…
Stop!
Atomic number
Mass number
Relative mass
Relative charge
Penetrating
Shielding
Complete the chart
on notebook paper,
then continue.
Nuclear Properties Table
Property
Greek Letter
Symbol
Actually is…
Atomic number
Mass number
Relative mass
Relative charge
Penetrating
Shielding
Alpha
Beta
Gamma
Nuclear Properties Table
Property
Greek Letter
Symbol
Actually is…
Atomic number
Mass number
Relative mass
Relative charge
Penetrating
Shielding
Alpha
Beta
Gamma
a
b
g
Nuclear Properties Table
Property
Greek Letter
Symbol
Actually is…
Atomic number
Mass number
Relative mass
Relative charge
Penetrating
Shielding
Alpha
Beta
Gamma
a
b
g
4
2He
0
-1e
NA
Nuclear Properties Table
Property
Greek Letter
Symbol
Actually is…
Atomic number
Mass number
Relative mass
Relative charge
Penetrating
Shielding
Alpha
Beta
Gamma
a
b
g
4
2He
0
-1e
NA
He nucleus
electron
EM energy
Nuclear Properties Table
Property
Greek Letter
Symbol
Actually is…
Atomic number
Mass number
Relative mass
Relative charge
Penetrating
Shielding
Alpha
Beta
Gamma
a
b
g
4
2He
0
-1e
NA
He nucleus
electron
EM energy
2
-1
NA
Nuclear Properties Table
Property
Alpha
Beta
Gamma
a
b
g
4
2He
0
-1e
NA
He nucleus
electron
EM energy
Atomic number
2
-1
NA
Mass number
4
0
NA
Greek Letter
Symbol
Actually is…
Relative mass
Relative charge
Penetrating
Shielding
Nuclear Properties Table
Property
Alpha
Beta
Gamma
a
b
g
4
2He
0
-1e
NA
He nucleus
electron
EM energy
Atomic number
2
-1
NA
Mass number
4
0
NA
Relative mass
4
1/
1837
NA
Greek Letter
Symbol
Actually is…
Relative charge
Penetrating
Shielding
Nuclear Properties Table
Property
Alpha
Beta
Gamma
a
b
g
4
2He
0
-1e
NA
He nucleus
electron
EM energy
Atomic number
2
-1
NA
Mass number
4
0
NA
Relative mass
4
1/
1837
NA
+2
-1
NA
Greek Letter
Symbol
Actually is…
Relative charge
Penetrating
Shielding
Nuclear Properties Table
Property
Alpha
Beta
Gamma
a
b
g
4
2He
0
-1e
NA
He nucleus
electron
EM energy
Atomic number
2
-1
NA
Mass number
4
0
NA
Relative mass
4
1/
1837
NA
+2
-1
NA
Low
Medium
High
Greek Letter
Symbol
Actually is…
Relative charge
Penetrating
Shielding
Nuclear Properties Table
Property
Alpha
Beta
Gamma
a
b
g
4
2He
0
-1e
NA
He nucleus
electron
EM energy
Atomic number
2
-1
NA
Mass number
4
0
NA
Relative mass
4
1/
1837
NA
+2
-1
NA
Low
Medium
High
Greek Letter
Symbol
Actually is…
Relative charge
Penetrating
Shielding
2.5 cm of air; Metal, plastic
anything else
or wood
Lead or
concrete
Protection from radiation
1. Shielding
2. Distance
How do you protect yourself from …
2.5 cm of air, paper, skin
aluminum, lead, other
Beta
metals, wood, plastic, etc.
Gamma up to a foot or two of lead,
many feet of concrete
Alpha
There are some kinds of
radiation you can not
protect your self from.
Radiation
Gamma rays and high energy
cosmic particles from space.
But there is one kind of
radiation hazard that you
can protect against.
That hazard comes from the
uranium beneath your feet.
Uranium in the ground
decays according to …
The uranium decay
series
Uranium-238
decays through
many steps to
make stable
lead-206
http://library.tedankara.k12.tr/chemistry/vol1/nucchem/trans90.htm
The uranium decay
series
Radon is
the only gas
in the series.
http://library.tedankara.k12.tr/chemistry/vol1/nucchem/trans90.htm
Hazards from radon
Since radon is the only gas in the
decay series of uranium …
…it can work its way up through
the ground and into your
basements and crawl spaces.
You breathe radon into your lungs.
Hazards from radon
And when radon is in your lungs…
…it can decay and release an
alpha particle …
…which travels only a short
distance before it is absorbed by
your lungs, and transfers its energy.
Hazards from radon
This ionizing radiation in your
lungs can cause lung cancer.
Smoking cigarettes and breathing
radon really increases your
chances of getting lung cancer.
Protecting against radon
Get a test kit to see if there is a
problem. Charcoal canisters,
which are sent off for analysis.
Abatement:
Seal places where gas gets in.
Ventilation – bring in fresh air.
Half life
What is half life?
Half life is the time needed for one
half of a radioisotope to decay.
Suppose you start with 100.0 grams
of a radioisotope that has a half life
of exactly 1 year.
What is half life?
How much will be left after 1 year?
Suppose you start with 100.0 grams
of a radioisotope that has a half life
of exactly 1 year.
What is half life?
After one year there will be 50.0 g left.
After a second year there will be
25.0 g left.
Suppose you start with 100.0 grams
of a radioisotope that has a half life
of exactly 1 year.
What is half life?
After one year there will be 50.0 g left.
After a second year there will be
25.0 g left.
After a third year there will
be 12.5 grams left.
After a fourth year there
will be 6.25 grams left.
Half life project
1. Pick a mass between 10g and 50g.
2. Decide on a half life – any time.
3. Scale your graph – mass on y-axis
and at least six (6) half-lives on
the x-axis.
4. Plot the masses after intervals of
one half-life.
Half life project
5. What shape is the graph?
6. When will the mass of the
radioisotope fall to zero?
7. When is the radioactivity no
longer a problem?
8. What mathematical function
describes radioactive decay?
Half life project
mass
10
5
2.5
time
t1/2
t1/2
Half life project
mass
10
5
2.5
time
t1/2
t1/2
Activity (counts/min)
Half life project
200
Exponential decay
-kt
e
A = A0
100
50
t1/2
Time (min)
t1/2
Activity (counts/min)
200
100
50
Half life project
Radiation is “not a
problem” when it falls
below background level.
background
t1/2
Time (min)
t1/2
Half life project
Questions:
1. A radioisotope has a half-life of
100 years. How long will it take for
the radiation to decrease to 1/16 of
its original value?
400 years
Half life project
Questions:
2. A radioisotope has an activity of
560 counts per minute. After 16
hours the count rate has dropped to
35 counts per minute. What is the
half life of the radioisotope?
4 hours
Decay equations
Alpha decay
In alpha decay, an alpha particle
4
(2He ) is released from the
nucleus.
The alpha particle carries away
two protons and two neutrons.
Alpha decay
decay product
238
U
92
2
4
He
+ 90
234
Th
alpha particle
The mass number
decreases by 4.
238
U
92
2
Alpha decay
4
He
234
Th
+ 90
The atomic number decreases by 2.
Alpha decay
These must add up to 238
238
U
92
2
4
He
234
Th
+ 90
These must add up to 92
Alpha decay
Radon-220 decays by alpha emission.
What is the decay product?
86
220
Rn
2
4
He
+
216
Po
84???
Alpha decay
Write the alpha decay equations for:
2
4
He
1.
241
Am
95
2.
216
84Po

4
He
2
3.
226
88Ra

4
He
2
237
Np
+
93
+
212
Pb
82
+ 86
222
Rn
Beta decay
Beta decay occurs because of the
instability of a neutron.
Neutrons are a little more massive
than protons; neutrons are neutral.
What does this suggest about the
composition of neutrons?
Beta decay
Scientists used to think that neutrons
might be a combination of a proton
and an electron.
We know that neutrons decay into
protons, which stay in the nucleus,
and electrons, which are ejected
from the nucleus as beta particles.
Beta decay
Decay of a neutron:
1
n
0
neutron

1
H
1
proton
+
0
e
-1
electron
The electron ejected from the
nucleus is a beta particle.
Beta decay
Technically, the decay of a neutron
also involves a neutrino.
1
0n
neutron
1
1
H
+
0
e
-1
proton electron
+
0
n
0
antineutrino
Beta decay
Actually, an anti-neutrino.
The word “neutrino” comes from Enrico
Fermi, meaning “little neutral one” in Italian.
1
0n
neutron
1
1
H
+
0
e
-1
proton electron
+
0
n
0
antineutrino
Beta decay
A neutrino is a particle with no
charge and almost no mass.
1
0n
neutron
1
1
H
+
0
e
-1
proton electron
+
0
n
0
antineutrino
Beta decay
A neutrino carries off some of the
energy in the decay of the neutron.
1
0n
neutron
1
1
H
+
0
e
-1
proton electron
+
0
n
0
antineutrino
Beta decay
When predicting the products of
beta decay we will ignore neutrinos.
1
0n
neutron
1
1
H
+
0
e
-1
proton electron
+
0
n
0
antineutrino
Start with a
Li atom with
3 protons and
4 neutrons.
Now there
are 4 protons
and 3 neutrons.
Beta decay
Suddenly a
neutron
decays!
A beta particle
goes zipping out of
the nucleus.
Beta decay
A neutron decays to make a proton.
The number of neutrons decreases by 1
The number of protons increases by 1
The mass number stays the same.
The atomic number increases by 1
Beta decay
decay product
6
14
C

7
14
N
0
e
+ -1
beta particle
Beta decay
The mass number
stays the same.
14
C
6

14
N
7
The atomic number
increases by 1.
+ -1
0
e
Beta decay
These add up to 14
6
14
C

7
14
N
0
e
+ -1
Notice that these add up to 6
Beta decay
Zn-69 decays by beta emission.
What is the decay product?
30
69
Zn
 -1
0
e
+
69
???
Ga
31
Beta decay
Write the beta decay equations for:
1.
214
Pb
82

-1
2.
62
27Co

0
e
-1
3.
113
???
Ag

47
0
e
0
e
-1
214
Bi
+
83
+
62
Ni
28
+ 48
113
Cd
Review: decay equations
Alpha:
Go down two on periodic table
Atomic number decreases by 2
Mass number decreases by 4
Beta:
Go up one on periodic table
Atomic number increases by 1
Mass number stays the same
Nuclear energy
All nuclear decay is accompanied by
a release of energy.
Alpha and beta particles have
high kinetic energies.
Gamma rays are electromagnetic
energy. All have enough energy to
ionize atoms.
Nuclear energy
An ion is a “charged atom” or group
of atoms.
Ionization occurs when
electrons are removed from
atoms by a, b or g radiation.
This can result in
damage to your body.
cancer
Nuclear energy
Forms of ionizing radiation are:
Alpha
Beta
Gamma
X-rays
Cosmic rays Neutrons Positrons
Ultraviolet light (UV) can cause cancer,
but it is not ionizing radiation.