June 2010 Pisgah Post Newsletter, Pisgah Presbyterian Church
Nuclear Chemistry Last revision: 100211 M. Jones Pisgah High School.
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Transcript of Nuclear Chemistry Last revision: 100211 M. Jones Pisgah High School.
Nuclear Chemistry
Last revision: 100211
M. Jones
Pisgah High School
Nuclear chemistry studies
1. Atomic theory2. Radioactivity3. Isotopes 4. Half-life 5. Decay equations6. 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.
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We know that parts of Dalton’s atomic theory are no longer valid in today’s modern Quantum Mechanical model of the atom.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
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.
The Crookes’ Tube
What we now call the cathode ray 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
William Crookes
The shadow of the Maltese cross indicates that cathode rays travel in straight lines and can be stopped by a solid object.
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.
William Crookes
Cathode Ray Tube
High voltageHigh voltage
Cathode Anode
Direction of cathode rays
+
High voltageHigh voltage
Cathode Anode
Direction of cathode rays
+
Magnet
Cathode Ray Tube
High voltageHigh voltage
Cathode Anode
+
Used by J. J. Thomson …to discover the
electron.
Cathode Ray Tube
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
He had discovered the electron.
In 1897 J. J. Thomson found that cathode rays are a basic building block of matter.
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.
J.J. Thomson and Cathode Rays
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”.
HighVoltage
Cast iron pot
Atomizer
Robert A. Millikan
Telescope
HighVoltage Telescope
Cast iron pot
Atomizer
Oil Drop
Parallel charged plates
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 10-28 gram
Robert A. Millikan
He is to the atom what Darwin is to evolution, Newton to mechanics, Faraday to electricity and Einstein to relativity.
Ernest Rutherford
John Campbell http://www.rutherford.org.nz/biography.htm
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.
Ernest Rutherford
Alpha scattering
Apparatus for investigating alpha scattering.
What some textbook authors call the “gold foil experiment.”
+Most of the alpha particles pass through undeflected.
Alpha scattering source
+Some positive alpha particles are repelled by the small, dense, positively charged nucleus.
sourceAlpha scattering
+
Alpha scattering source
Some positive alpha particles are repelled by the small, dense, positively charged nucleus.
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.
Alpha scattering
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.
Ernest Rutherford
N + O + H
N + O + H
7 protons
2 protons
1 proton
8 protons
9 protons9 protons
Ernest Rutherford
We now know…
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.
Ernest Rutherford
Radioactivity
Demonstrations with radioactivity
Investigate the properties of Alpha, Beta and Gamma
Radiation
Mica window (fragile)
Wire (+ side of circuit)
Metal shield (- side)
Low pressure Ar gas
Counter 2435
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
Geiger-Mueller Tube
Radioactivity
• Alpha particles • Beta particles • Gamma rays
- helium nuclei- electrons - high energy
electromagnetic energy - similar to light, but higher in energy.
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.
Radioactivity
Has no charge.
- 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.
Radioactivity
Mass number /Atomic number
EA
Z
Mass number
Symbol of Element
Atomic number
protons + neutrons
Protons in nucleus
Mass number
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
Radioactivity
Alpha () particles are the nuclei of helium atoms and have the symbol
2He4.
What is the mass number of
an particle?2 He4
Radioactivity
How many times heavier is an alpha particle than a
hydrogen atom?
4
Alpha () particles are the nuclei of helium atoms and have the symbol
2He4.
Radioactivity
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
Radioactivity
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
Radioactivity
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.
Radioactivity
LocationLocationLocation
What 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.
Radioactivity
Gamma () 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.
Radioactivity
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.
Radiation
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.
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
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
U235
92
Mass number
Symbol of Element
Atomic number
protons + neutrons
Protons in nucleus
Mass number
Subatomic particles
H1
1 e0
-1
n10proton
neutronelectron
What do the numbers represent?
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 particles1. 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 particles6. 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 particles9. 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 …
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)
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 t1/2
Half life projectm
ass
time
10
52.5
t1/2 t1/2 t1/2
Half life project
time
10
52.5
t1/2 t1/2 t1/2Act
ivit
y (c
ount
s/m
in)
Exponential decay
A = A0e-kt
Half life project
time
10
52.5
t1/2 t1/2 t1/2Act
ivit
y (c
ount
s/m
in)
background
Radiation is “not a problem” when it falls below background level.
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 decayThe 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
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
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 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
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.
…the nucleus shouldn’t even exist!
Did you ever wonder ...
Because of the electrostatic repulsion…
The strong force.
Did you ever wonder ...
There must be a force that is stronger than the electrostatic repulsion.
The strong force is the force that holds the quarks together to make
protons and neutrons.
Did you ever wonder ...
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 mysteryCalculate the mass of the Fe-56 atom in
amu from the sum of the parts:Protons: 26 x 1.0073 = 26.189
Electrons: 26 x 0.000549 = 0.014Neutrons: 30 x 1.0087 = 30.261
Total mass = 56.465But! 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
Mass spectrometer
http://www.chemistry.ccsu.edu/glagovich/teaching/472/ms/instrumentation.html
magneticfield
Magnetic field makes charged atoms curve.
http://www.chemistry.ccsu.edu/glagovich/teaching/472/ms/instrumentation.html
magneticfield
Here’s a mystery
56.465 – 55.935 = 0.530 amu
The sum of the protons, neutrons and electrons is 56.465 amu.
but,
The actual mass is 55.935 amu.
Here’s a mystery
Where is the missing mass?
56.465 – 55.935 = 0.530 amuSum of parts: p+, n, e-
actual isotope
mass ?
The solution
What does it tell us?
Recall Einstein’s famous equation:
E = mc2
Matter and energy are equivalent.
The solution
Matter can exist as energy and …… energy can exist as matter.
All calculated from E = mc2
They are both the same “thing”.
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 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 the nucleus absorbs a neutron.
Nuclear fission
The mass number of the atom increases and the nucleus
becomes unstable.
A neutron collides with a nucleus and is absorbed.
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 unstable nucleus 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