Transcript Nuclear Chemistry

Nuclear
Chemistry
M. Jones
Pisgah High School
Last revision: 100211
Nuclear chemistry studies
1.
2.
3.
4.
5.
6.
Atomic theory
Radioactivity
Isotopes
Half-life
Decay equations
Energy, fission and fusion
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.
Dalton’s Atomic Theory
1. Atoms are tiny, discrete particles
2. Atoms are indestructible
3. Atoms of the same element have the
same mass and properties
4. Atoms combine in simple wholenumber ratios
5. Atoms in different ratios produce
different compounds.
Dalton’s Atomic Theory
1. Atoms are tiny, discrete particles
2. Atoms are indestructible
3. Atoms of the same element have the
same mass and properties
4.
in simple
wholeWeAtoms
knowcombine
that parts
of Dalton’s
number
ratiosare no longer valid in
atomic
theory
5.
Atomsmodern
in different
ratios produce
today’s
Quantum
different compounds.
Mechanical model of the atom.
Dalton’s Atomic Theory
1. Atoms are tiny, discrete particles
2. Atoms are indestructible
3. 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.
William Crookes
Used spectroscopy to discover
thallium and used vacuums to
measure its mass.
Invented the radiometer.
Improved vacuum systems.
Used by Edison to make light bulbs.
William Crookes
What we now
call the
cathode ray
tube.
The Crookes’ Tube
William Crookes
Used the cathode ray tube to to
study electric fields in a vacuum
and discovered rays, …
which were called “cathode rays”
by Goldstein, since they came
from the cathode, or negative
electrode.
William Crookes
The shadow of the Maltese cross indicates
that cathode rays travel in straight lines and
can be stopped by a solid object.
William Crookes
He found that the cathode rays
could be deflected by a magnet.
This suggested that the cathode
rays might be a stream of
electrically charged particles.
Cathode Ray Tube
Direction of
cathode rays
Cathode
Anode
High voltage
+
Cathode Ray Tube
Magnet
Direction of
cathode rays
Cathode
Anode
High voltage
+
Cathode Ray Tube
Used by J. J. Thomson …
to discover the
electron.
Cathode
Anode
High voltage
+
J.J. Thomson and Cathode Rays
• Attracted to positive electrode
• Thought might be atoms
• Had same charge to mass ratio regardless of
metal in the cathode
• The particle was much less massive than the
lightest element – H
• Particle must be common to all matter, a
subatomic particle
J.J. Thomson and Cathode Rays
In 1897 J. J. Thomson found that
cathode rays are a basic building
block of matter.
He had discovered the electron.
J.J. Thomson and Cathode Rays
The term “electron” comes from George
Stoney’s term for the “minimum electrical
charge”.
Thomson concluded that this particle was the
carrier of the minimum electrical charge and
so the particle was later called an “electron”.
J.J. Thomson and Cathode Rays
Even though Crookes and others observed
cathode rays, Thomson is credited with
the discovery of the electron because he
recognized that it was a fundamental
particle of nature as well as a sub-atomic
particle.
J.J. Thomson and Cathode Rays
Measured the charge to mass ratio,
and found …
… that if this “minimum charge” was
equal to the charge on a hydrogen ion,
then the mass of the electron would be
1/1837th the mass of a hydrogen atom.
J.J. Thomson and Cathode Rays
If that were the case, then the electron
would be much smaller than the smallest
atom ..… showing for the first time that
matter is made up of particles
smaller than atoms.
Thomson tried to measure the fundamental
charge on the electron.
Robert A. Millikan
Robert A. Millikan, an American
physicist, set out to determine the
charge on an electron.
From 1909 through 1910, he
performed what is now called the
“Oil Drop Experiment”.
Robert A. Millikan
Atomizer
High
Voltage
Telescope
Cast iron pot
Robert A. Millikan
Atomizer
Parallel
charged
plates
High
Voltage
Oil Drop
Telescope
Cast iron pot
Robert A. Millikan
Radiation stripped electrons from the oil
droplets. The charged droplets fell between
two electrically charged plates. By adjusting
the voltage, he could change the rate of fall or
rise of a single oil drop. After observing
hundreds of drops, he calculated the charge on
a single electron.
Robert A. Millikan
Charges on drops are multiples of
1.602 x 10-19 coulombs.
Robert A. Millikan
The fundamental charge on an electron is
1.602 x 10-19 coulombs.
With J. J. Thomson’s charge to mass ratio,
and Millikan’s charge on the electron, we are
able to compute the mass of an electron:
9.109 x
-28
10
gram
Ernest Rutherford
He is to the atom what
Darwin is to evolution,
Newton to mechanics,
Faraday to electricity and
Einstein to relativity.
John Campbell http://www.rutherford.org.nz/biography.htm
Ernest Rutherford
He moved from New Zealand to Cambridge University in
England (1895) where he pioneered the detection of
electromagnetic waves, but was lured away by J.J. Thomson
on work that would lead to the discovery of the electron.
The invention of radio communications went to Marconi,
instead. He later switched to working with radioactivity
(1896) and discovered alpha and beta rays. He went to
Montreal to teach at McGill University (1898) where he
continued his work on radioactivity with Frederick Soddy,
and others (1898-1907). He moved back to back to England
to teach at Manchester (1907). He received the Nobel prize
in chemistry in 1908 for his work on radioactivity in Canada.
Ernest Rutherford
In 1907, he and a student, Hans Geiger, developed what
would later become the “Geiger counter”. While at McGill,
Rutherford discovered that after alpha rays passed through a
thin film of mica, the image formed on a photographic plate
was “fuzzy”. He and Geiger began a project to investigate
the scattering of alpha particles by thin films. Rutherford
later gave Ernest Marsden, an undergraduate, his own
research project which was to look for evidence of the
backscatter of alphas (1909). To their surprise, Marsden
found that some alpha particles were scattered backwards
from thin films of lead, platinum, tin, silver, copper, iron,
aluminum, and gold.
Ernest Rutherford
Rutherford remarked that it was like firing a navel gun at a
piece of tissue paper and the shell bouncing back and hitting
you. By 1910, Hans Geiger had finished his research on the
forward scattering of alpha particles but he could not
reconcile it with Marsden’s observations of the backscatter of
alphas. The problem was passed on to Rutherford, who
came up with the answer, and the astounding results were
published in 1911.
Ernest Rutherford
Rutherford had discovered a new piece to the atomic puzzle,
the nucleus. According to Rutherford, the positively charged
alpha particles were encountering a tiny, positively charged
particle within the atoms of the metal and were being
repelled. The atoms themselves appeared to mostly empty
space. It was the repulsion of two positively charged
particles which caused the scattering observed by Geiger and
Marsden. Rutherford had found that atoms are mostly empty
space with a small, dense, positively charged nucleus.
Alpha scattering
Apparatus for
investigating
alpha scattering.
What some textbook
authors call the “gold foil
experiment.”
a source
Alpha scattering
+
Most of the alpha
particles pass
through undeflected.
a source
Alpha scattering
+
Some positive alpha
particles are repelled
by the small, dense,
positively charged
nucleus.
a source
Alpha scattering
+
Some positive alpha
particles are repelled
by the small, dense,
positively charged
nucleus.
Alpha scattering
Alpha particles are repelled by a small,
dense, positively charged nucleus.
Almost all the mass of an atom is in the
nucleus. Atoms are mostly empty space.
Electrons are located outside the
nucleus.
Published results in 1911.
Ernest Rutherford
Rutherford, during the First World War, worked on
developing SONAR and submarine detection, but still found
time to tinker with alpha radiation. In 1917 he bombarded
nitrogen gas with alpha particles and discovered that oxygen
and hydrogen were produced. Rutherford had resorted to
alchemy and accomplished the first transmutation of one
element into another. He had also indirectly discovered the
proton.
N+a  O+H
Ernest Rutherford
We now know…
N+a  O+H
7 protons
2 protons
9 protons
1 proton
8 protons
9 protons
Ernest Rutherford
Rutherford concluded that the nucleus must contain the
positively charged protons in a number equal to the negative
charge from the electrons, but this did not account for all of
the mass of the atom. He, along with James Chadwick,
rejected the idea that there must be additional protons and
electrons in the nucleus, and concluded that there must be a
neutral particle in the nucleus that accounted for the
additional mass. In 1932, Chadwick confirmed the existence
of the neutron.
Radioactivity
Demonstrations with
radioactivity
Investigate the properties of
Alpha, Beta and Gamma
Radiation
Geiger-Mueller Tube
Counter
2435
Wire (+ side of circuit)
Metal shield (- side)
Low pressure Ar gas
Mica window (fragile)
Geiger-Mueller Tube
Rays leave the source
Some hit the GM tube
Most do nothing
One ray may cause a
discharge…
Source
and the detector clicks
Geiger-Mueller Tube
• Filled 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
Radioactivity
• Alpha particles  a - helium nuclei
• Beta particles  b - electrons
• Gamma rays  g - high energy
electromagnetic
energy - similar
to light, but
higher in energy.
Radioactivity
Alpha particles
An unstable nucleus splits to form a
more stable nucleus an an alpha particle.
An alpha particle is the
nucleus of a helium atom.
Two protons and two neutrons.
Has a +2 charge.
Radioactivity
Beta particles
Ejected from the nucleus when
a neutron decays.
A beta particle is identical
to an electron
Has a -1 charge.
Radioactivity
Gamma rays
Emitted by an unstable nucleus
as it becomes more stable
Electromagnetic energy with short
wavelengths and high energy.
Has no charge.
Radioactivity
- comes from the natural decay of unstable
atoms.
- can be detected by photographic film,
scintillation detector or a Geiger counter.
- is “ionizing radiation”. Causes cell damage
and mutations – cancer.
- is protected against by shielding and
distance.
Mass number /Atomic number
Mass number
Protons in
nucleus
Z
Atomic number
E
A
protons
+ neutrons
Mass number
Symbol of
Element
Mass number /Atomic number
Mass number
Protons in
nucleus
U
92
Atomic number
235
protons
+ neutrons
Mass number
Symbol of
Element
Radioactivity
Alpha (a) particles are the nuclei of
helium atoms and have the symbol
4.
He
2
What is the atomic
number of an a
particle?
2
4
He
Radioactivity
Alpha (a) particles are the nuclei of
helium atoms and have the symbol
4.
He
2
What is the
mass number of
an a particle?
2
4
He
Radioactivity
Alpha (a) particles are the nuclei of
helium atoms and have the symbol
4.
He
2
How many times heavier is
an alpha particle than a
hydrogen atom?
4
Radioactivity
Beta (b) particles are high speed
electrons ejected from the nuclei of
atoms and have the symbol -1e0.
What is the mass
number of a b
particle?
-1
0
e
Radioactivity
Beta (b) particles are high speed
electrons ejected from the nuclei of
atoms and have the symbol -1e0.
No protons or
neutrons in an
electron.
-1
0
e
Radioactivity
Beta (b) particles are high speed
electrons ejected from the nuclei of
atoms and have the symbol -1e0.
What is the difference
between a b particle and a
“regular” electron?
None
Radioactivity
Beta (b) particles are high speed
electrons ejected from the nuclei of
atoms and have the symbol -1e0.
What is the difference
between a b particle and a
“regular” electron?
Location
Location
Location
Radioactivity
Gamma (g) rays are high energy
electromagnetic waves, not particles.
No protons, neutrons or electrons.
Gamma rays have short wavelengths, 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
Radiation
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.
Atomic Theory
We know that atoms are mostly
empty space.
We know that atoms are made up
of protons, neutrons and electrons.
Protons and neutrons are located in
a small, dense, positively charged
nucleus.
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
Geiger and Marsden’s work in alpha
scattering (gold foil experiment ).
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.
Mass number /Atomic number
Mass number
Protons in
nucleus
U
92
Atomic number
235
protons
+ neutrons
Mass number
Symbol of
Element
Subatomic particles
1
0
proton
1
1
H
n
neutron
electron
e
-1
0
What do the numbers represent?
Property
Symbols
Proton
Neutron
Electron
Location
Rel. mass
Mass (amu)
Mass (g)
Rel. charge
Charge (C)
Fill in the chart
with the correct
information.
Property Proton
+ and H1
p
Symbols
1
Location
Rel. mass
Mass (amu)
Mass (g)
Rel. charge
Charge (C)
Neutron
Electron
n0 and 0n1
e- and -1e0
Property Proton
+ and H1
p
Symbols
1
Location
Rel. mass
Mass (amu)
Mass (g)
Rel. charge
Charge (C)
nucleus
Neutron
Electron
n0 and 0n1
e- and -1e0
nucleus
cloud outside
nucleus
Property Proton
+ and H1
p
Symbols
1
Neutron
Electron
n0 and 0n1
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
+ and H1
p
Symbols
1
Neutron
Electron
n0 and 0n1
e- and -1e0
Location
nucleus
nucleus
cloud outside
nucleus
Rel. mass
1
1
1/
1837
Mass (amu) 1.0073 amu
Mass (g)
Rel. charge
Charge (C)
1.0087 amu 0.00549 amu
Property Proton
+ and H1
p
Symbols
1
Neutron
Electron
n0 and 0n1
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
Rel. charge
Charge (C)
9.11x10-29
Property Proton
+ and H1
p
Symbols
1
Neutron
Electron
n0 and 0n1
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
Rel. charge
Charge (C)
+1
0
9.11x10-29
-1
Property Proton
+ and H1
p
Symbols
1
Neutron
Electron
n0 and 0n1
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
Rel. charge
+1
Charge (C) +1.6x10-19 C
9.11x10-29
0
-1
0
-1.6x10-19 C
Subatomic particles
1. 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.
Subatomic particles
6. Protons and neutrons are each made
of smaller particles called quarks.
7. Quarks are elementary particles just
like electrons. They are not
composed of smaller particles.
8. There are six kinds of quarks:
“up”, “down”, “top”, “bottom”,
“charm” and “strange”.
Subatomic particles
9. Protons are composed of two “up
quarks” and one “down quark”.
10. Neutrons are composed of two
“down quarks” and one “up quark”.
11. Quarks are held together to make
protons and neutrons by the strong
force, the strongest of the four
fundamental forces in nature.
Gravity, electromagnetism, weak and strong.
Isotopes
Isotopes …
…of the same element have the
same number of protons and
electrons but different numbers of
neutrons.
Therefore, isotopes of the same
element have different masses.
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 …
…have different mass numbers but
the same atomic number.
Atomic number - the number of
protons in the nucleus of an atom.
Mass number - the sum of the
protons and neutrons in the nucleus.
Symbols for Isotopes
Mass number
A is the
symbol
A
for mass Z
number
Atomic
number
E
Symbol
of
Element
Z is the symbol for
atomic number
Symbols for Isotopes
Mass number
235
92
Atomic
number
U
Symbol
of
Element
An isotope of uranium
Symbols for Isotopes
Mass number
This form solves
the word processor
dilemma.
U
92
Atomic
number
235
Symbol of
Element
An isotope of uranium
Symbols for Isotopes
Symbol of
Element
Find U in the periodic
table.
U-235
How do you know
the atomic number?
Z = 92
Mass number
Some elements have several
Isotopes
Lead has four naturally occurring
isotopes, Pb-204, Pb-206, Pb-207,
and Pb-208; but there are 23 manmade 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 atomic number is the
number of protons in the nucleus.
The number of electrons in a
neutral atom equals the
number of protons.
Finding the number of Protons,
Neutrons, and Electrons
The number of neutrons is the
difference between the mass
number and the atomic number.
neutrons = A - Z
Finding the number of Protons,
Neutrons, and Electrons
U-235
Z = 92
protons = 92
electrons = 92
Look at the periodic
table and find the
element by using the
symbol.
A = 235
protons + neutrons = 235
Finding the number of Protons,
Neutrons, and Electrons
U-235
How many
neutrons
are
in
a
Z = 92
U-235
atom?
protons = 92
electrons = 92
A = 235
protons + neutrons = 235
Finding the number of Protons,
Neutrons, and Electrons
U-235
How many
neutrons
are
in
a
Z = 92
U-235
atom?
protons = 92
electrons = 92
235 – 92 = 143 neutrons
Finding the number of Protons,
Neutrons, and Electrons
Q. Find the number of
neutrons in the Ba-137 isotope.
A. In the Ba-137 isotope …
… Z = 56 and A = 137
137 – 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
Zinc
A
#p
#n
#e
66
In
68
85
38
82 210
Rn
136
35
47
Finding the number of Protons, Neutrons, and Electrons
Element
Zinc
Stop!66
Complete
the 68
In
85
table, then go
82 210
on.
Rn
136
Symbol Z
A
#p
35
#n
47
#e
38
Finding the number of Protons, Neutrons, and Electrons
Element
Symbol Z
Zinc
A
#p
#n
#e
66
In
68
85
38
82 210
Rn
136
35
47
Finding the number of Protons, Neutrons, and Electrons
Element
Zinc
Symbol Z
Zn
30
A
#p
#n
#e
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
66
Zinc
Zn
30
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
66
Zinc
Zn
30
30
36
30
Indium
In
49 117 49
68
49
Strontium
Sr
38
47
38
85
38
82 210
Rn
136
35
47
Finding the number of Protons, Neutrons, and Electrons
Element
Symbol Z
A
#p
#n
#e
66
Zinc
Zn
30
30
36
30
Indium
In
49 117 49
68
49
Strontium
Sr
38
47
38
Lead
Pb
82 210 82 128 82
85
38
Rn
136
35
47
Finding the number of Protons, Neutrons, and Electrons
Element
Symbol Z
A
#p
#n
#e
66
Zinc
Zn
30
30
36
30
Indium
In
49 117 49
68
49
Strontium
Sr
38
47
38
Lead
Pb
82 210 82 128 82
Radon
Rn
86 222 86 136 86
85
38
35
47
Finding the number of Protons, Neutrons, and Electrons
Element
Symbol Z
A
#p
#n
#e
66
Zinc
Zn
30
30
36
30
Indium
In
49 117 49
68
49
Strontium
Sr
38
47
38
Lead
Pb
82 210 82 128 82
Radon
Rn
86 222 86 136 86
Bromine
Br
35
85
82
38
35
47
35
Atomic mass is the weighted average
of all the isotopes of an element
Boron has two isotopes:
B-10
19.8% 10.01 amu
B-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 amu
Si-29
4.67% 28.976 amu
Si-30
3.10% 29.974 amu
0.9223 x 27.977 + 0.0467 x 28.976 + 0.0310 x 29.974 =
28.086 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 ??.?? % 34.97 amu
Cl - 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 amu
Cl - 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
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.
2.
3.
4.
5.
6.
The atomic number of 12
The number of protons and electrons
The number of neutrons
The atomic weight of 24.986 AMU
The reaction with hydrochloric acid
The speed of gaseous Mg atoms
Which of the following is the same for the
three isotopes of magnesium?
1. The atomic number of 12
Same
All three isotopes of
magnesium have the same
atomic number.
Which of the following is the same for the
three isotopes of magnesium?
2. The number of protons and
electrons
Same
All isotopes of the same element
have the same number of protons
in the nucleus, and electrons
outside the nucleus.
Which of the following is the same for the
three isotopes of magnesium?
3. The number of neutrons
Not the same
The number of neutrons varies
with the isotope. Different
isotopes have different numbers
of neutrons.
Which of the following is the same for the
three isotopes of magnesium?
4. Atomic weight of 24.986 AMU
Not the same
Mg-24  23.985 AMU
Mg-25  24.986 AMU
Mg-26  25.983 AMU
Which of the following is the same for the
three isotopes of magnesium?
5. The reaction with HCl
Same
All isotopes of the same element
react the same chemically.
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
Not the same
The speeds of atoms depend on
mass.
Heavier atoms move more slowly,
and lighter atoms move faster.
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
Graham’s law
Gaseous diffusion
Enriched uranium
Manhattan Project
Manhattan Project
Naturally occurring
uranium is mostly U-238
Less than 1% of naturally
occurring uranium is U-235
Manhattan Project
To sustain a nuclear chain
reaction, uranium must be at
least 4% U-235.
Bomb grade uranium is
over 90% U-235
Manhattan Project
The uranium for a nuclear
reactor is around 4% U-235.
The process of increasing
the percentage of U-235 is
called enrichment.
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.
r
M
1
r2

2
M1
Manhattan Project
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.
Uranium Pellet
Fuel rod
assembly
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.
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
t1/2 t1/2 t1/2
time
Half life project
mass
10
5
2.5
t1/2 t1/2 t1/2
time
Activity (counts/min)
Half life project
10
Exponential decay
-kt
e
A = A0
5
2.5
t1/2 t1/2 t1/2
time
Activity (counts/min)
Half life project
10
5
2.5
Radiation is “not a
problem” when it falls
below background level.
background
t1/2 t1/2 t1/2
time
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
The conversion of a neutron to a
proton involves the “weak” force.
An “up” quark flips to become a
“down” quark. When this occurs a
high energy electron (beta) and an
antineutrino are produced, both of
which leave the nucleus.
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
Gamma rays
Gamma radiation is often emitted
along with alpha and beta radiation.
When a decay event occurs,
“extra” energy is sometimes
left in the nucleus.
Gamma rays
The “extra” energy in the decay
product is released as gamma
radiation. This lowers the energy of
the nucleus and makes it more
stable.
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
What holds the
nucleus together?
Did you ever wonder ...
Why the nucleus stays together with
all those positively charged protons
in such a small space?
Protons have a positive charge
and objects with like charges
repel each other.
Why do they
look like this?
Each hair has
the same
charge.
Did you ever wonder ...
Because of the
electrostatic repulsion…
…the nucleus
shouldn’t even exist!
Did you ever wonder ...
There must be a force that is
stronger than the electrostatic
repulsion.
The strong force.
Did you ever wonder ...
The strong force is the force that
holds the quarks together to make
protons and neutrons.
The residual strong force extends from
the quarks in a proton or neutron to the
quarks in an adjacent proton or neutron
and holds the nucleus together.
There is a closely
related mystery.
Here’s a mystery
Consider the iron-56 isotope.
It has a mass of 55.935 amu.
How many protons, neutrons and
electrons?
26 protons
30 neutrons
26 electrons
Here’s a mystery
Calculate the mass of the Fe-56 atom in
amu from the sum of the parts:
Protons: 26 x 1.0073 = 26.189
Neutrons: 30 x 1.0087 = 30.261
Electrons: 26 x 0.000549 = 0.014
Total mass = 56.465
But! The actual mass is 55.935
Here’s a mystery
The actual mass of an isotope can
be found using a device called a
mass spectrometer.
The actual mass is 55.935
http://www.chemistry.ccsu.edu/glagovich/teaching/472/ms/instrumentation.html
Mass spectrometer
magnetic
field
http://www.chemistry.ccsu.edu/glagovich/teaching/472/ms/instrumentation.html
Magnetic field makes
charged atoms curve.
magnetic
field
Here’s a mystery
The sum of the protons, neutrons
and electrons is 56.465 amu.
but,
The actual mass is 55.935 amu.
56.465 – 55.935 = 0.530 amu
Here’s a mystery
56.465 – 55.935 = 0.530 amu
Sum of
parts:
p+, n, e-
actual
isotope
mass
?
Where is the missing mass?
The solution
Recall Einstein’s famous equation:
E=
2
mc
What does it tell us?
Matter and energy are equivalent.
The solution
Matter can exist as energy and …
… energy can exist as matter.
They are both the same “thing”.
All calculated from E =
2
mc
The solution
The difference between the
mass of the parts (p+, n and e-)
and the actual mass is called
the “mass defect” and equals
the mass of nuclear material
that “exists as energy”.
The solution
The energy from the missing mass
is the binding energy of the
nucleus.
The binding energy is derived
from the strong force which does
hold the nucleus together.
The solution
The binding energy is the energy
required to “take apart” the
nucleus to form nothing but
individual protons and neutrons.
Is this binding energy
related to nuclear
energy?
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.
There’s even more!
Some of the energy that holds the
nucleus together is carried away by
the alpha, beta and gamma radiation.
But there is an even greater release of
energy when the atom splits apart …
Nuclear Fission
Nuclear fission
Fission – the splitting of
an atom after the nucleus
absorbs a neutron.
Nuclear fission
A neutron collides with a nucleus
and is absorbed.
The mass number of the atom
increases and the nucleus
becomes unstable.
Nuclear fission
The unstable nucleus splits into
two or more fission fragments.
Plus, two or three neutrons are
released along with a great deal of
energy. The neutrons strike other
atoms causing more fission.
Nuclear fission
Fission fragment
U-235
Neutrons
U-235
Neutron
Fission fragment
U-235
Nuclear fission
These U-235 atoms
can split when hit
U-235
by
neutrons,
and
Neutrons
release more
neutrons, starting a
U-235
chain reaction.
Fission fragment
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
As the chain reaction proceeds,
energy is released as heat energy.
This energy originally held
the nucleus together.
Billions of splitting atoms releases
a huge amount of 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
Containment
building
Nuclear reactor
Reactor core
Heat exchanger
Steam generator
Steam to
turbine
Water from
cooling lake
Water circulates in the core
Containment
building
Nuclear reactor
Cadmium
control
rods
Reactor core
– absorb neutrons
Steam to
turbine
Water from
cooling lake
Water circulates in the core
Containment
building
The water in the core
Nuclear
reactor
serves two
functions.
(1)
The
water
cools
the
core
Reactor core
and carries away heat.
(2) Water is a moderator.
to the
The waterSteam
slows
turbine
neutrons so that they can
cause fission. Fast
neutrons
Water
from
cooling
lake
do not cause
fission.
Water circulates in the core
Containment
building
Nuclear reactor
Reactor core
Water from
cooling lake
Water circulates in the core
Containment
building
Nuclear reactor
Reactor core
Heat exchanger
Steam generator
Water from
cooling lake
Water circulates in the core
Containment
building
Nuclear reactor
Reactor core
Heat exchanger
Steam generator
Water from
cooling lake
Water circulates in the core
Containment
building
Nuclear reactor
Reactor core
Heat exchanger
Steam generator
Steam to
turbine
Water from
cooling lake
Water circulates in the core
From nuclear energy to…
Heat exchanger
Steam generator
Transmission wires
generator
Steam to turbine
turbine
Condensed steam
Water from
cooling lake
Cooling towers
or lake
Electrical energy
Heat exchanger
Steam generator
Transmission wires
generator
Steam to turbine
turbine
Condensed steam
Water from
cooling lake
Cooling towers
or lake
Electrical energy
Heat
Thisexchanger
part of
Steam generator
Transmission
wires
the system
is the
same regardless of how the steam
is produced.
The heatgenerator
can come
Steam to turbine
turbine
from nuclear energy
or by steam
Condensed
burning
Watercoal,
from natural gas or fuel
Cooling towers
oil. cooling lake
or lake
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, onsite storage, breeder reactors,
transportation of spent fuel, “not
in my backyard”, …
What about fusion?
Nuclear fusion
A day without
sunshine
is like a day
without fusion.
Nuclear fusion
Nuclear fusion powers the sun.
Fusion occurs when hydrogen
atoms combine to make helium,
and release energy.
Is nuclear fusion an alternative to
fission for producing electricity?
Nuclear fusion
Fusion not now technically feasible.
Occurs at very high temperatures
which nothing can withstand.
Magnetic bottle. Control problems.
Now consumes more energy
than it releases.
Nuclear Chemistry
Developed by Mike Jones
Pisgah High School
Canton, NC