Nuclear Chemistry Last revision: 110409 M. Jones Pisgah High School.
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Transcript of Nuclear Chemistry Last revision: 110409 M. Jones Pisgah High School.
Nuclear Chemistry
Last revision: 110409
M. Jones
Pisgah High School
Atomic Theory
Atomic Theory
Atoms are the smallest particles of elements.
Atoms were first proposed by Democritus over 2000 years ago.
The idea of atoms was reintroduced in 1803 by John Dalton.
1. Atoms are tiny, discrete particles 2. Atoms are indestructible3. Atoms of the same element have the
same mass and properties4. Atoms combine in simple whole-
number ratios5. Atoms in different ratios produce
different compounds.
Dalton’s Atomic Theory
1. Atoms are tiny, discrete particles 2. Atoms are indestructible3. Atoms of the same element have the
same mass and properties4. Atoms combine in simple whole-
number ratios5. Atoms in different ratios produce
different compounds.
We know that parts of Dalton’s atomic theory are no longer valid in today’s modern Quantum Mechanical model of the atom.
Dalton’s Atomic Theory
1. Atoms are tiny, discrete particles 2. Atoms are indestructible3. Atoms of the same element have the
same mass and properties
We know that atoms are made up of smaller particles, and that there are slight differences between atoms of the same element - isotopes.
Dalton’s Atomic Theory
Atomic Theory
We know that atoms are made up of protons, neutrons and electrons.
Protons and neutrons are located in a small, dense, positively charged nucleus.
We know that atoms are mostly empty space.
Atomic Theory
In 1897 J. J. Thomson discovered that cathode rays were actually streams of subatomic particles.
These particles carried a negative charge and were called electrons.
Cathode ray tube
Atomic Theory
We know atoms are mostly empty space and that protons and neutrons
are located in a small, dense, positively charged nucleus because of Rutherford’s explanation of the
alpha scattering (gold foil) experiment.
+Most of the alpha particles pass through undeflected.
Atomic Theory source
+Some positive alpha particles are repelled by the small, dense, positively charged nucleus.
Atomic Theory source
Atomic Theory
We know that electrons are outside the nucleus in an “electron cloud”.
Electrons exist in specific energy levels, which explains the line
spectra of the elements.
Started with the Bohr model.
Atomic Theory
We now use the Quantum Mechanical Model of the atom.
Quantum Theory describes the nature of electrons and their
interactions with the electrons of other atoms in chemical reactions.
Atomic Theory
The subatomic particles that make up atoms have known properties like mass and electrical charge.
Our understanding came through the efforts of a number of
scientists like Thomson, Millikan, Rutherford, and Chadwick.
Property Proton Neutron Electron
Symbols
Location
Rel. mass
Mass (amu)
Mass (g)
Rel. charge
Charge (C)
Fill in the chart with the correct information.
Property Proton Neutron Electron
Symbols p+ and 1H1 n0 and 0n
1 e- and -1e0
Location
Rel. mass
Mass (amu)
Mass (g)
Rel. charge
Charge (C)
Property Proton Neutron Electron
Symbols p+ and 1H1 n0 and 0n
1 e- and -1e0
Location nucleus nucleus cloud outside nucleus
Rel. mass
Mass (amu)
Mass (g)
Rel. charge
Charge (C)
Property Proton Neutron Electron
Symbols p+ and 1H1 n0 and 0n
1 e- and -1e0
Location nucleus nucleus cloud outside nucleus
Rel. mass 1 1 1/1837
Mass (amu)
Mass (g)
Rel. charge
Charge (C)
Property Proton Neutron Electron
Symbols p+ and 1H1 n0 and 0n
1 e- and -1e0
Location nucleus nucleus cloud outside nucleus
Rel. mass 1 1 1/1837
Mass (amu) 1.0073 amu 1.0087 amu 0.00549 amu
Mass (g)
Rel. charge
Charge (C)
Property Proton Neutron Electron
Symbols p+ and 1H1 n0 and 0n
1 e- and -1e0
Location nucleus nucleus cloud outside nucleus
Rel. mass 1 1 1/1837
Mass (amu) 1.0073 amu 1.0087 amu 0.00549 amu
Mass (g) 1.673x10-24 1.675x10-24 9.11x10-29
Rel. charge
Charge (C)
Property Proton Neutron Electron
Symbols p+ and 1H1 n0 and 0n
1 e- and -1e0
Location nucleus nucleus cloud outside nucleus
Rel. mass 1 1 1/1837
Mass (amu) 1.0073 amu 1.0087 amu 0.00549 amu
Mass (g) 1.673x10-24 1.675x10-24 9.11x10-29
Rel. charge +1 0 -1
Charge (C)
Property Proton Neutron Electron
Symbols p+ and 1H1 n0 and 0n
1 e- and -1e0
Location nucleus nucleus cloud outside nucleus
Rel. mass 1 1 1/1837
Mass (amu) 1.0073 amu 1.0087 amu 0.00549 amu
Mass (g) 1.673x10-24 1.675x10-24 9.11x10-29
Rel. charge +1 0 -1
Charge (C) +1.6x10-19 C 0 -1.6x10-19 C
Subatomic particles - Summary1. Protons and neutrons are located in
the nucleus.2. Protons and neutrons have almost
the same mass. Neutrons heavier.3. Electrons are outside the nucleus and
much lighter than proton or neutron.4. Protons and electrons have the same
charge but opposite polarity. 5. Neutrons have no charge.
Isotopes
Isotopes …
Therefore, isotopes of the same element have different masses.
…of the same element have the same number of protons and electrons but different numbers of neutrons.
Isotopes …
…don’t have to be radioactive. Some isotopes are unstable and
decay, releasing alpha or beta particles, or gamma rays.
But, there are many stable isotopes that don’t decay.
Isotopes …
Mass number - the sum of the protons and neutrons in the nucleus.
Atomic number - the number of protons in the nucleus of an atom.
…have different mass numbers but the same atomic number.
Symbols for Isotopes
EA
Z
Symbol of Element
Mass number
Atomic number
A is the symbol for mass number
Z is the symbol for atomic number
U235
92
Symbols for Isotopes
Symbol of Element
Mass number
Atomic number
An isotope of uranium
Symbols for Isotopes
U235
92
Mass number
Symbol of Element
Atomic number
An isotope of uranium
This form solves the word processor dilemma.
U-235
Symbol of Element
Mass number
How do you know the atomic number?
Find U in the periodic table.
Symbols for Isotopes
Z = 92
Some elements have several Isotopes
Lead has four naturally occurring isotopes, Pb-204, Pb-206, Pb-207, and Pb-208; but there are 23 man-made isotopes of lead.
Some elements have several Isotopes
Bismuth has only one naturally occurring isotope,
Bi-209, but there are 22 man-made isotopes of bismuth.
Finding the number of Protons, Neutrons, and Electrons
The number of electrons in a neutral atom equals the
number of protons.
The atomic number is the number of protons in the nucleus.
neutrons = A - Z
The number of neutrons is the difference between the mass number and the atomic number.
Finding the number of Protons, Neutrons, and Electrons
Look at the periodic table and find the element by using the symbol.
U-235
A = 235protons + neutrons = 235
Z = 92protons = 92electrons = 92
Finding the number of Protons, Neutrons, and Electrons
U-235
A = 235protons + neutrons = 235
Z = 92protons = 92electrons = 92
Finding the number of Protons, Neutrons, and Electrons
How many neutrons are in a U-235 atom?
U-235
235 – 92 = 143 neutrons
Z = 92protons = 92electrons = 92
Finding the number of Protons, Neutrons, and Electrons
How many neutrons are in a U-235 atom?
Q. Find the number of neutrons in the Ba-137 isotope.
A. In the Ba-137 isotope …… Z = 56 and A = 137137 – 56 = 81 neutrons
Finding the number of Protons, Neutrons, and Electrons
Copy the following table on notebook paper, and
fill in the blanks.
Finding the number of Protons, Neutrons, and Electrons
Element Symbol Z A #p #n #e
Zinc 66
In 68
85 38
82 210
Rn 136
35 47
Finding the number of Protons, Neutrons, and Electrons
Element Symbol Z A #p #n #e
Zinc 66
In 68
85 38
82 210
Rn 136
35 47
Stop!Complete the table, then go
on.
Finding the number of Protons, Neutrons, and Electrons
Element Symbol Z A #p #n #e
Zinc 66
In 68
85 38
82 210
Rn 136
35 47
Finding the number of Protons, Neutrons, and Electrons
Element Symbol Z A #p #n #e
Zinc Zn 30 66 30 36 30
In 68
85 38
82 210
Rn 136
35 47
Finding the number of Protons, Neutrons, and Electrons
Element Symbol Z A #p #n #e
Zinc Zn 30 66 30 36 30
Indium In 49 117 49 68 49
85 38
82 210
Rn 136
35 47
Finding the number of Protons, Neutrons, and Electrons
Element Symbol Z A #p #n #e
Zinc Zn 30 66 30 36 30
Indium In 49 117 49 68 49
Strontium Sr 38 85 38 47 38
82 210
Rn 136
35 47
Finding the number of Protons, Neutrons, and Electrons
Element Symbol Z A #p #n #e
Zinc Zn 30 66 30 36 30
Indium In 49 117 49 68 49
Strontium Sr 38 85 38 47 38
Lead Pb 82 210 82 128 82
Rn 136
35 47
Finding the number of Protons, Neutrons, and Electrons
Element Symbol Z A #p #n #e
Zinc Zn 30 66 30 36 30
Indium In 49 117 49 68 49
Strontium Sr 38 85 38 47 38
Lead Pb 82 210 82 128 82
Radon Rn 86 222 86 136 86
35 47
Finding the number of Protons, Neutrons, and Electrons
Element Symbol Z A #p #n #e
Zinc Zn 30 66 30 36 30
Indium In 49 117 49 68 49
Strontium Sr 38 85 38 47 38
Lead Pb 82 210 82 128 82
Radon Rn 86 222 86 136 86
Bromine Br 35 82 35 47 35
Finding the number of Protons, Neutrons, and Electrons
Atomic mass is the weighted average of all the isotopes of an
element
Boron has two isotopes:B-10 19.8% 10.01 amuB-11 80.2% 11.01 amu
0.198 x 10.01 + 0.802 x 11.01 = 10.81 amu
Atomic mass is the weighted average of all the isotopes of an
element
Determine the atomic mass of silicon:Si-28 92.23% 27.977 amuSi-29 4.67% 28.976 amuSi-30 3.10% 29.974 amu
0.9223 x 27.977 + 0.0467 x 28.976 + 0.0310 x 29.974 = 28.086 amu
Consider the two isotopes of chlorine. Which isotope is more abundant?Cl - 35 ??.?? % 34.97 amuCl - 37 ??.?? % 36.97 amu
The average atomic mass is 35.453 amu.
Atomic mass is the weighted average of all the isotopes of an
element
Consider the two isotopes of chlorine. Which isotope is more abundant?Cl - 35 75.85% 34.97 amuCl - 37 24.15% 36.97 amu
The average atomic mass is 35.453 amu.
Atomic mass is the weighted average of all the isotopes of an
element
Which isotope of neon is more abundant? Ne-20 or Ne-22
Atomic mass is the weighted average of all the isotopes of an
element
Ne-20 90%Ne-22 10%
How are isotopes of the same element alike and different?
Alike:
1. Number of protons and electrons
2. Atomic number
3. Chemical properties
Different:
1. Number of neutrons
2. Mass Number
3. Atomic mass of the isotopes
Which of the following is the same for the three isotopes of magnesium?
1. The atomic number of 122. The number of protons and electrons3. The number of neutrons4. The atomic weight of 24.986 AMU5. The reaction with hydrochloric acid6. The speed of gaseous Mg atoms
1. The atomic number of 12
All three isotopes of magnesium have the same atomic number.
Same
Which of the following is the same for the three isotopes of magnesium?
2. The number of protons and electrons
All isotopes of the same element have the same number of protons in the nucleus, and electrons outside the nucleus.
Same
Which of the following is the same for the three isotopes of magnesium?
3. The number of neutrons
The number of neutrons varies with the isotope. Different isotopes have different numbers of neutrons.
Not the same
Which of the following is the same for the three isotopes of magnesium?
4. Atomic weight of 24.986 AMU
Mg-24 23.985 AMU
Mg-25 24.986 AMU
Mg-26 25.983 AMU
Not the same
Which of the following is the same for the three isotopes of magnesium?
5. The reaction with HCl
All isotopes of the same element react the same chemically.
Same
The number and arrangement of electrons is the same for each isotope.
Which of the following is the same for the three isotopes of magnesium?
6. The speed of gaseous Mg atoms
The speeds of atoms depend on mass.
Heavier atoms move more slowly, and lighter atoms move faster.
Not the same
Which of the following is the same for the three isotopes of magnesium?
How did knowing about Graham’s Law allow the United States to win World War II?
Who were the two guys responsible for winning World War II?
Fat Man, and … Little Boy
Atomic bombs dropped on Hiroshima and Nagasaki
Hiroshima
Nagasaki
Manhattan Project
Oak Ridge, TN
Gaseous diffusion
Graham’s law
Enriched uranium
Manhattan Project
Less than 1% of naturally occurring uranium is U-235
Manhattan Project
Naturally occurring uranium is mostly U-238
To sustain a nuclear chain reaction, uranium must be at least 4% U-235.
Manhattan Project
Bomb grade uranium is over 90% U-235
The process of increasing the percentage of U-235 is
called enrichment.
The uranium for a nuclear reactor is around 4% U-235.
Manhattan Project
Uranium ore is reacted with fluorine to make gaseous UF6.
Then the gaseous UF6 is introduced into chambers with porous disks in the ends.
Manhattan Project
The lighter UF6 molecules containing U-235 effuse
through the holes in the disk faster. There is more U-235
on the other side of disk.
Manhattan Project
As the UF6 continues to move through many, many disks, the percentage of U-235 atoms in the gas increases, resulting in
enrichment.
Manhattan Project
Graham’s Law says that gas molecules which weigh less, will move faster than molecules which weigh more.
Manhattan Project
1
2
2
1
r
r
M
M
The enriched UF6 containing a much higher percentage of U-235 atoms, is reacted with water to make uranium oxide and HF. The uranium oxide is dried and made into fuel pellets.
Manhattan Project
Uranium Pellet
Fuel rod assembly
Only one element has unique names for its isotopes …
tritium H
deuterium H
hydrogen H
31
21
11
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
Cobalt-59 occurs naturally. When a neutron “sticks” to the nucleus,
cobalt-60 is formed.
Man-made isotopes are usually made by bombarding atoms with protons or neutrons.
Uses for Isotopes
Radioisotopes are used as tracers in chemical reactions.
Radioisotopes are used in “imaging” living and nonliving systems.
Radioisotopes are used to kill cancer cells. (Co-60, Bi-212)
Demonstrations with radioactivity
Recall what you have discovered about nuclear radiation.
Mica window (fragile)
Wire (+ side of circuit)Metal shield (- side)Low pressure Ar gas
Counter 2435
Geiger-Mueller Tube
GM Tube
Rays leave the sourceSome hit the GM tube
Most do nothing
One ray may cause a discharge…
Source and the detector clicks
GM TubeFilled with low pressure argon gas
About 1% efficiency
About 1 in 100 rays causes an electric spark between the case and the wire
Each spark registers as a count or click on the counter
Properties of alpha, beta and gamma
radiation
Subatomic particles
H1
1 e0
-1
n10proton
neutronelectron
What do the numbers represent?
Mass number /Atomic number
U235
92
Mass number
Symbol of Element
Atomic number
protons + neutrons
Protons in nucleus
Mass number
Alpha () particles are the nuclei of helium atoms and have the symbol 2He4.
What is the atomic number
of an particle?2 He4
Alpha () particles are the nuclei of helium atoms and have the symbol 2He4.
How many times heavier is an alpha particle than
a hydrogen atom?4
Beta () particles are high speed electrons ejected from the nuclei of atoms and have the symbol -1e0.What is the mass number of a particle?
-1e0
Beta () particles are high speed electrons ejected from the nuclei of atoms and have the symbol -1e0.
No protons or neutrons in an electron. -1e0
Beta () particles are high speed electrons ejected from the nuclei of atoms and have the symbol -1e0.
NoneWhat is the difference between a particle and a “regular” electron?
Beta () particles are high speed electrons ejected from the nuclei of atoms and have the symbol -1e0.
LocationLocationLocation
What is the difference between a particle and a “regular” electron?
Gamma () 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
… and high energies.
Increasing energy
Alpha, Beta, Gamma
Radioactive Source
- - - - - - - - -
+ + + + + + + +
Electric field from electrically charged plates
What is the effect of an electric field on
Alpha, Beta, Gamma
Radioactive Source
- - - - - - - - -
+ + + + + + + +
Electric field from electrically charged plates
Alpha, Beta, Gamma
Radioactive Source
- - - - - - - - -
+ + + + + + + +
Are , and rays deflected by magnetic fields?
Electric field from electrically charged plates
Radioactive Source
Paper
Aluminum foil
Lead
Alpha, Beta, Gamma
Radioactive Source
Paper
Aluminum foil
Lead
Alpha, Beta, Gamma
Radioactive Source
Paper
Aluminum foil
Lead
Alpha, Beta, Gamma
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) Greek letter
(2) symbol
(3) actually is
(4) atomic number
(5) mass number
(6) relative mass
(7) relative. charge
(8) penetrating ability
(9) shielding
Nuclear Properties TableProperty Alpha Beta Gamma
Greek Letter
Symbol
Actually is…
Atomic number
Mass number
Relative mass
Relative charge
Penetrating
Shielding
Stop!Complete the chart on notebook paper,
then continue.
Nuclear Properties TableProperty Alpha Beta Gamma
Greek Letter
Symbol
Actually is…
Atomic number
Mass number
Relative mass
Relative charge
Penetrating
Shielding
Nuclear Properties TableProperty Alpha Beta Gamma
Greek Letter Symbol
Actually is…
Atomic number
Mass number
Relative mass
Relative charge
Penetrating
Shielding
Nuclear Properties TableProperty Alpha Beta Gamma
Greek Letter Symbol
2He4-1e0 NA
Actually is…
Atomic number
Mass number
Relative mass
Relative charge
Penetrating
Shielding
Nuclear Properties TableProperty Alpha Beta Gamma
Greek Letter Symbol
2He4-1e0 NA
Actually is… He nucleus electron EM energy
Atomic number
Mass number
Relative mass
Relative charge
Penetrating
Shielding
Nuclear Properties TableProperty Alpha Beta Gamma
Greek Letter Symbol
2He4-1e0 NA
Actually is… He nucleus electron EM energy
Atomic number 2 -1 NA
Mass number
Relative mass
Relative charge
Penetrating
Shielding
Nuclear Properties TableProperty Alpha Beta Gamma
Greek Letter Symbol
2He4-1e0 NA
Actually is… He nucleus electron EM energy
Atomic number 2 -1 NA
Mass number 4 0 NA
Relative mass
Relative charge
Penetrating
Shielding
Nuclear Properties TableProperty Alpha Beta Gamma
Greek Letter Symbol
2He4-1e0 NA
Actually is… He nucleus electron EM energy
Atomic number 2 -1 NA
Mass number 4 0 NA
Relative mass 4 1/1837NA
Relative charge
Penetrating
Shielding
Nuclear Properties TableProperty Alpha Beta Gamma
Greek Letter Symbol
2He4-1e0 NA
Actually is… He nucleus electron EM energy
Atomic number 2 -1 NA
Mass number 4 0 NA
Relative mass 4 1/1837NA
Relative charge +2 -1 NA
Penetrating
Shielding
Nuclear Properties TableProperty Alpha Beta Gamma
Greek Letter Symbol
2He4-1e0 NA
Actually is… He nucleus electron EM energy
Atomic number 2 -1 NA
Mass number 4 0 NA
Relative mass 4 1/1837NA
Relative charge +2 -1 NA
Penetrating Low Medium High
Shielding
Nuclear Properties TableProperty Alpha Beta Gamma
Greek Letter Symbol
2He4-1e0 NA
Actually is… He nucleus electron EM energy
Atomic number 2 -1 NA
Mass number 4 0 NA
Relative mass 4 1/1837NA
Relative charge +2 -1 NA
Penetrating Low Medium High
Shielding 2.5 cm of air;anything else
Metal, plastic or wood
Lead or concrete
Protection from radiation1. Shielding 2. Distance
How do you protect yourself from …
Alpha
Beta
Gamma
2.5 cm of air, paper, skinaluminum, lead, other metals, wood, plastic, etc.up to a foot or two of lead, many feet of concrete
There are some kinds of radiation you can not
protect your self from.
Gamma rays and high energy cosmic particles from space.
But there is one kind of radiation hazard that you
can protect against.
Radiation
That hazard comes from the uranium beneath your feet.
Uranium in the ground decays according to …
Uranium-238 decays through
many steps to make stable
lead-206
The uranium decay series
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.
Suppose you start with 100.0 grams of a radioisotope that has a half life
of exactly 1 year.
After a second year there will be 25.0 g left.
What is half life?
After a third year there will be 12.5 grams left.
After one year there will be 50.0 g left. After a second year there will be
25.0 g left.
After a fourth year there will be 6.25 grams left.
Half life project1. 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 project5. 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 projectm
ass
time
10
52.5
t1/2 t1/2
Half life projectm
ass
time
2.5
t1/2 t1/2
10
5
Half life projectA
ctiv
ity
(cou
nts/
min
)
Time (min)
200
10050
t1/2 t1/2
Exponential decay
A = A0e-kt
Half life project
Time (min)
10050
t1/2 t1/2A
ctiv
ity
(cou
nts/
min
)
background
Radiation is “not a problem” when it falls below background level.
200
Half life projectQuestions:
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 projectQuestions:
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 (2He4) is released from the nucleus.
The alpha particle carries away two protons and two neutrons.
Alpha decay
92U238 2He4 + 90Th234
alpha particle
decay product
Alpha decay
92U238 2He4 + 90Th234
The atomic number decreases by 2.
The mass number decreases by 4.
Alpha decay
These must add up to 238
These must add up to 92
92U238 2He4 + 90Th234
Alpha decay
86Rn220 2He4 + ???
Radon-220 decays by alpha emission. What is the decay product?
84Po216
Alpha decay
Write the alpha decay equations for:
1. 95Am241
2. 84Po216
3. 88Ra226
2He4 + 93Np237
2He4 + 82Pb212
2He4 + 86Rn222
Beta decay
Neutrons are a little more massive than protons; neutrons are neutral.
What does this suggest about the composition of neutrons?
Beta decay occurs because of the instability of a neutron.
Beta decayScientists 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
0n1 1H1 + -1e0
neutron proton electron
The electron ejected from the nucleus is a beta particle.
Decay of a neutron:
Beta decay
0n1 1H1 + -1e0 + 00
neutron proton electron
Technically, the decay of a neutron also involves a neutrino.
anti-neutrino
Beta decay
0n1 1H1 + -1e0 + 00
neutron proton electron
Actually, an anti-neutrino.
anti-neutrino
The word “neutrino” comes from Enrico Fermi, meaning “little neutral one” in Italian.
Beta decay
0n1 1H1 + -1e0 + 00
neutron proton electron
A neutrino is a particle with no charge and almost no mass.
anti-neutrino
Beta decay
0n1 1H1 + -1e0 + 00
neutron proton electron
A neutrino carries off some of the energy in the decay of the neutron.
anti-neutrino
Beta decay
0n1 1H1 + -1e0 + 00
neutron proton electron
When predicting the products of beta decay we will ignore neutrinos.
anti-neutrino
Beta decayStart with a Li atom with
3 protons and 4 neutrons.
Suddenly a neutron decays!
Now there are 4 protons
and 3 neutrons.
A beta particle goes zipping out of
the nucleus.
Beta decay
The number of neutrons
The number of protons
The mass number
The atomic number
A neutron decays to make a proton.
decreases by 1
increases by 1
stays the same.
increases by 1
Beta decay
6C14 7N14 + -1e0
beta particle
decay product
Beta decay
6C14 7N14 + -1e0
The atomic number increases by 1.
The mass number stays the same.
Beta decay
6C14 7N14 + -1e0
Notice that these add up to 6
These add up to 14
Beta decay
Zn-69 decays by beta emission. What is the decay product?
30Zn69 -1e0 + ??? 31Ga69
Beta decay
Write the beta decay equations for:
1. 82Pb214
2. 27Co62
-1e0 + 83Bi214
-1e0 + 28Ni62
3. ??? -1e0 + 48Cd11347Ag113
Review: decay equationsAlpha:
Go down two on periodic tableAtomic number decreases by 2Mass number decreases by 4
Beta:Go up one on periodic tableAtomic number increases by 1Mass number stays the same
Nuclear energy
All have enough energy to ionize atoms.
Gamma rays are electromagnetic energy.
Alpha and beta particles have high kinetic energies.
All nuclear decay is accompanied by a release of energy.
Nuclear energy
This can result in damage to your body.
Ionization occurs when electrons are removed from
atoms by or radiation.
An ion is a “charged atom” or group of atoms.
cancer
Nuclear energy
Forms of ionizing radiation are:
Alpha Beta Gamma X-rays
Cosmic rays
Ultraviolet light (UV) can cause cancer, but it is not ionizing radiation.
Neutrons Positrons
There’s even more!
But there is an even greater release of energy when the atom splits apart …
Some of the energy that holds the nucleus together is carried away by the alpha, beta and gamma radiation.
Nuclear Fission
Nuclear fission
Fission – the splitting of an atom after being struck by a neutron.
Nuclear fission
The neutrons strike other atoms causing more fission.
Plus, two or three neutrons are released along with a great deal of energy.
The atom splits into two or more fission fragments.
U-235U-235
U-235
Nuclear fission
NeutronNeutrons
Fission fragment
Fission fragment
Nuclear fission
U-235
U-235
Neutrons
Fission fragment
These U-235 atoms can split when hit by neutrons, and
release more neutrons, starting a
chain reaction.
Nuclear fission
To picture a chain reaction, imagine 50 mousetraps in a wire cage.
And on each mousetrap are two ping-pong balls.
Now imagine dropping one more ping-pong ball into the cage …
Detail of ping-pong balls on mousetraps.
http://www.physics.montana.edu/demonstrations/video/modern/demos/mousetrapchainreaction.html
http://www.physics.montana.edu/demonstrations/video/modern/demos/mousetrapchainreaction.html
Nuclear fission
Billions of splitting atoms releases a huge amount of heat energy.
This energy originally held the nucleus together.
As the chain reaction proceeds, energy is released as heat energy.
Nuclear fission
This heat energy can be harnessed to boil water, creating steam,
that can spin a turbine,
that can turn a generator,
creating electricity.
Nuclear reactor
Nuclear reactor
Nuclear reactorReactor core
Containment building
Fue
l rod
s
Heat exchangerSteam generator
Water circulates in the core
Steam to turbine
Water from cooling lake
Water from cooling lake
Nuclear reactorReactor core
Containment building
Fue
l rod
s
Water circulates in the core
Steam to turbine
Cadmium control rods – absorb neutrons
Water from cooling lake
Nuclear reactorReactor core
Fue
l rod
s
Water circulates in the core
Steam to turbine
The water in the core serves two functions.
(1) The water cools the core and carries away heat.
(2) Water is a moderator. The water slows the
neutrons so that they can cause fission. Fast
neutrons do not cause fission.
Containment building
Nuclear reactorReactor core
Containment building
Fue
l rod
s
Water circulates in the core
Water from cooling lake
Nuclear reactorReactor core
Containment building
Fue
l rod
s
Water circulates in the core
Water from cooling lake
Heat exchangerSteam generator
Nuclear reactorReactor core
Containment building
Fue
l rod
s
Water circulates in the core
Water from cooling lake
Heat exchangerSteam generator
Nuclear reactorReactor core
Containment building
Fue
l rod
s
Water circulates in the core
Water from cooling lake
Steam to turbine
Heat exchangerSteam generator
From nuclear energy to…
Steam to turbine
Water from cooling lake Cooling towers
or lake
turbine generator
Transmission wires
Condensed steam
Heat exchangerSteam generator
Steam to turbine
Water from cooling lake Cooling towers
or lake
turbine generator
Transmission wires
Condensed steam
Heat exchangerSteam generator
Electrical energy
Steam to turbine
Water from cooling lake Cooling towers
or lake
turbine generator
Transmission wires
Condensed steam
Heat exchangerSteam generator
Electrical energy
This part of the system is the same regardless of how the steam is produced. The heat can come from nuclear energy or by burning coal, natural gas or fuel oil.
Electrical energy
In fact, the only purpose of a nuclear reactor is to boil water.
Pros and cons
Cheap, plentiful power, no CO2, nuclear waste, terrorist attack, running out of oil and coal, on-site storage, breeder reactors, transportation of spent fuel, “not in my backyard”, …
What about fusion?
Nuclear fusion
is like a day without fusion.
A day without sunshine
Nuclear fusion
Is nuclear fusion an alternative to fission for producing electricity?
Fusion occurs when hydrogen atoms combine to make helium,
and release energy.
Nuclear fusion powers the sun.
Nuclear fusion
Now consumes more energy than it releases.
Magnetic bottle. Control problems.
Occurs at very high temperatures which nothing can withstand.
Fusion not now technically feasible.
Nuclear Chemistry
Developed by Mike JonesPisgah High School
Canton, NC