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Nuclear Chemistry. M. Jones Pisgah High School. Last revision: 100211. Nuclear chemistry studies. Atomic theory Radioactivity Isotopes Half-life Decay equations Energy, fission and fusion. Atomic Theory. Atomic Theory. Atoms are the smallest particles of elements.

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nuclear chemistry

Nuclear Chemistry

M. Jones

Pisgah High School

Last revision: 100211

nuclear chemistry studies
Nuclear chemistry studies
  • Atomic theory
  • Radioactivity
  • Isotopes
  • Half-life
  • Decay equations
  • Energy, fission and fusion
slide3
Atomic

Theory

slide4
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.

slide5
Dalton’s Atomic Theory
  • Atoms are tiny, discrete particles
  • Atoms are indestructible
  • Atoms of the same element have the same mass and properties
  • Atoms combine in simple whole-number ratios
  • Atoms in different ratios produce different compounds.
slide6
Dalton’s Atomic Theory
  • Atoms are tiny, discrete particles
  • Atoms are indestructible
  • Atoms of the same element have the same mass and properties
  • Atoms combine in simple whole-number ratios
  • 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We know that parts of Dalton’s atomic theory are no longer valid in today’s modern Quantum Mechanical model of the atom.

slide7
Dalton’s Atomic Theory
  • Atoms are tiny, discrete particles
  • Atoms are indestructible
  • 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
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 crookes1
William Crookes

What we now call the cathode ray tube.

The Crookes’ Tube

william crookes2
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 crookes3
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 crookes4
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
Cathode Ray Tube

Direction of cathode rays

Cathode

Anode

+

High voltage

cathode ray tube1
Cathode Ray Tube

Magnet

Direction of cathode rays

Cathode

Anode

+

High voltage

cathode ray tube2
Cathode Ray Tube

Used by J. J. Thomson …

to discover the electron.

Cathode

Anode

+

High voltage

j j thomson and cathode rays
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 rays1
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.

the term electron comes from george stoney s term for the minimum electrical charge
The term “electron” comes from George Stoney’s term for the “minimum electrical charge”.

J.J. Thomson and Cathode Rays

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 rays2
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 rays3
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 rays4
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

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 millikan1
Robert A. Millikan

Atomizer

High

Voltage

Telescope

Cast iron pot

robert a millikan2
Robert A. Millikan

Atomizer

Parallel charged plates

High

Voltage

Oil Drop

Telescope

Cast iron pot

robert a millikan3
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 millikan4
Robert A. Millikan

Charges on drops are multiples of

1.602 x 10-19 coulombs.

robert a millikan5
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

slide28
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

slide29
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.

slide30
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.

slide31
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.

slide32
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.

slide33
Alpha scattering

Apparatus for investigating alpha scattering.

What some textbook authors call the “gold foil experiment.”

slide34
+

Alpha scattering

a source

Most of the alpha particles pass through undeflected.

slide35
+

Alpha scattering

a source

Some positive alpha particles are repelled by the small, dense, positively charged nucleus.

slide36
+

Alpha scattering

a source

Some positive alpha particles are repelled by the small, dense, positively charged nucleus.

slide37
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.

slide38
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

slide39
7 protons

1 proton

2 protons

8 protons

9 protons

9 protons

Ernest Rutherford

We now know…

N + a O + H

slide40
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.

demonstrations with radioactivity
Demonstrations with radioactivity

Investigate the properties of

Alpha, Beta and Gamma

Radiation

geiger mueller tube
Wire (+ side of circuit)

Metal shield (- side)

Low pressure Ar gas

Mica window (fragile)

Geiger-Mueller Tube

Counter

2435

geiger mueller tube1
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 tube2
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
Radioactivity
  • Alpha particles
  • Beta particles
  • Gamma rays
  • a
  • b
  • g
  • helium nuclei
  • electrons
  • high energy electromagnetic energy - similar to light, but higher in energy.
radioactivity1
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.

radioactivity2
Radioactivity

Beta particles

Ejected from the nucleus when a neutron decays.

A beta particle is identical to an electron

Has a -1 charge.

radioactivity3
Radioactivity

Gamma rays

Emitted by an unstable nucleus as it becomes more stable

Electromagnetic energy with short wavelengths and high energy.

Has no charge.

radioactivity4
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.

slide51
Mass number

protons

+ neutrons

Protons in nucleus

Mass number

Symbol of Element

Atomic number

Mass number /Atomic number

E

A

Z

slide52
Mass number

protons

+ neutrons

Protons in nucleus

Mass number

Symbol of Element

Atomic number

Mass number /Atomic number

U

235

92

slide53
Radioactivity

Alpha (a) particles are the nuclei of helium atoms and have the symbol 2He4.

2 He4

What is the atomic number of an a particle?

slide54
Radioactivity

Alpha (a) particles are the nuclei of helium atoms and have the symbol 2He4.

2 He4

What is the mass number of an a particle?

slide55
Radioactivity

Alpha (a) particles are the nuclei of helium atoms and have the symbol 2He4.

4

How many times heavier is an alpha particle than a hydrogen atom?

slide56
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?

-1e0

slide57
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.

-1e0

slide58
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

slide59
Radioactivity

Beta (b) particles are high speed electrons ejected from the nuclei of atoms and have the symbol -1e0.

Location

Location

Location

What is the difference between a b particle and a “regular” electron?

slide60
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.

slide61
Increasing energy

Gamma rays have short wavelengths

… and high energies.

slide62
+ + + + + + + +

Alpha, Beta, Gamma

Electric field from electrically charged plates

What is the effect of an electric field on a, b, g ?

- - - - - - - - -

Radioactive Source

slide63
+ + + + + + + +

Alpha, Beta, Gamma

Electric field from electrically charged plates

b

g

a

- - - - - - - - -

Radioactive Source

slide64
+ + + + + + + +

Alpha, Beta, Gamma

Electric field from electrically charged plates

b

Are a, b and g rays deflected by magnetic fields?

g

a

- - - - - - - - -

Radioactive Source

slide65
Alpha, Beta, Gamma

Paper

Lead

a

Aluminum foil

Radioactive Source

slide66
Alpha, Beta, Gamma

Paper

Lead

b

a

Aluminum foil

Radioactive Source

slide67
Alpha, Beta, Gamma

Paper

Lead

b

g

a

Aluminum foil

Radioactive Source

radiation project
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
Greek letter

symbol

actually is

atomic number

mass number

relative mass

relative. charge

penetrating ability

shielding

Properties to include in your table:
slide70
Nuclear Properties Table

Stop!

Complete the chart on notebook paper, then continue.

protection from radiation
Protection from radiation
  • Shielding 2. Distance

How do you protect yourself from …

Alpha

Beta

Gamma

2.5 cm of air, paper, skin

aluminum, lead, other metals, wood, plastic, etc.

up to a foot or two of lead, many feet of concrete

radiation
Radiation

Gamma rays and high energy cosmic particles from space.

But there is one kind of radiation hazard that you can protect against.

slide84
That hazard comes from the uranium beneath your feet.

Uranium in the ground decays according to …

slide85
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

slide86
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
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 radon1
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 radon2
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
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.

slide91
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.

slide92
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 ).

slide93
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.

slide94
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.

slide95
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.

slide96
Mass number

protons

+ neutrons

Protons in nucleus

Mass number

Symbol of Element

Atomic number

Mass number /Atomic number

U

235

92

slide97
n

1

0

H

1

1

e

0

-1

Subatomic particles

proton

electron

neutron

What do the numbers represent?

slide106
Subatomic particles
  • Protons and neutrons are located in the nucleus.
  • Protons and neutrons have almost the same mass. Neutrons heavier.
  • Electrons are outside the nucleus and much lighter than proton or neutron.
  • Protons and electrons have the same charge but opposite polarity.
  • Neutrons have no charge.
slide107
Subatomic particles
  • Protons and neutrons are each made of smaller particles called quarks.
  • Quarks are elementary particles just like electrons. They are not composed of smaller particles.
  • There are six kinds of quarks:
  • “up”, “down”, “top”, “bottom”, “charm” and “strange”.
slide108
Subatomic particles
  • Protons are composed of two “up quarks” and one “down quark”.
  • Neutrons are composed of two “down quarks” and one “up quark”.
  • 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.
slide110
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.

slide111
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.

slide112
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.

slide113
Mass number

Symbol of Element

Atomic number

Symbols for Isotopes

A is the symbol for mass number

A

E

Z

Z is the symbol for atomic number

slide114
Mass number

Symbol of Element

Atomic number

Symbols for Isotopes

235

U

92

An isotope of uranium

slide115
Mass number

Symbol of Element

Atomic number

Symbols for Isotopes

This form solves the word processor dilemma.

U

235

92

An isotope of uranium

slide116
Symbol of Element

Mass number

Symbols for Isotopes

Find U in the periodic table.

Z = 92

U-235

How do you know the atomic number?

slide117
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.

slide118
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
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 electrons1
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 electrons2
Finding the number of Protons, Neutrons, and Electrons

Look at the periodic table and find the element by using the symbol.

U-235

Z = 92

protons = 92

electrons = 92

A = 235

protons + neutrons = 235

finding the number of protons neutrons and electrons3
Finding the number of Protons, Neutrons, and Electrons

How many neutrons are in a U-235 atom?

U-235

Z = 92

protons = 92

electrons = 92

A = 235

protons + neutrons = 235

finding the number of protons neutrons and electrons4
Finding the number of Protons, Neutrons, and Electrons

How many neutrons are in a U-235 atom?

U-235

Z = 92

protons = 92

electrons = 92

235 – 92 = 143 neutrons

slide124
Finding the number of Protons, Neutrons, and Electrons

Q. Find the number of neutrons in the Ba-137 isotope.

  • In the Ba-137 isotope …
  • … Z = 56 and A = 137
  • 137 – 56 = 81 neutrons
slide125
Finding the number of Protons, Neutrons, and Electrons

Copy the following table on notebook paper, and fill in the blanks.

slide127
Finding the number of Protons, Neutrons, and Electrons

Stop!

Complete the table, then go on.

slide135
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

slide136
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

slide137
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.

slide138
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.

slide139
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:

Number of protons and electrons

Atomic number

Chemical properties

Different:

Number of neutrons

Mass Number

Atomic mass of the isotopes

How are isotopes of the same element alike and different?
which of the following is the same for the three isotopes of magnesium
Which of the following is the same for the three isotopes of magnesium?
  • 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 magnesium1
Which of the following is the same for the three isotopes of magnesium?
  • 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 magnesium2
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 magnesium3
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 magnesium4
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 magnesium5
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 magnesium6
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.

slide149
Who were the two guys responsible for winning World War II?

Fat Man, and …

Little Boy

Atomic bombs dropped on Hiroshima and Nagasaki

slide152
Manhattan Project

Oak Ridge, TN

Graham’s law

Gaseous diffusion

Enriched uranium

slide154
Manhattan Project

Naturally occurring uranium is mostly U-238

Less than 1% of naturally occurring uranium is U-235

slide155
Manhattan Project

To sustain a nuclear chain reaction, uranium must be at least 4% U-235.

Bomb grade uranium is over 90% U-235

slide156
Manhattan Project

The uranium for a nuclear reactor is around 4% U-235.

The process of increasing the percentage of U-235 is calledenrichment.

slide157
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.

slide158
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.

slide159
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.

slide160
Manhattan Project

Graham’s Law says that gas molecules which weigh less, will move faster than molecules which weigh more.

slide161
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.

slide162
Uranium Pellet

Fuel rod assembly

only one element has unique names for its isotopes
Only one element has unique names for its isotopes …

Deuterium and tritium are used in nuclear reactors and fusion research.

some isotopes are radioactive
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

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
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.

what is 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 life1
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 life2
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 life3
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
Half life project
  • Pick a mass between 10g and 50g.
  • Decide on a half life – any time.
  • Scale your graph – mass on y-axis and at least six (6) half-lives on the x-axis.
  • Plot the masses after intervals of one half-life.
half life project1
Half life project
  • What shape is the graph?
  • When will the mass of the radioisotope fall to zero?
  • When is the radioactivity no longer a problem?
  • What mathematical function describes radioactive decay?
half life project2
mass

time

t1/2

t1/2

t1/2

Half life project

10

5

2.5

half life project3
mass

time

t1/2

t1/2

t1/2

Half life project

10

5

2.5

half life project4
t1/2

t1/2

t1/2

Half life project

10

Exponential decay

A = A0e-kt

5

Activity (counts/min)

2.5

time

half life project5
t1/2

t1/2

t1/2

Half life project

10

Radiation is “not a problem” when it falls below background level.

5

Activity (counts/min)

background

2.5

time

half life project6
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 project7
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

alpha decay
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 decay1
decay product

alpha particle

Alpha decay

92U238  2He4 + 90Th234

alpha decay2
The mass number decreases by 4.

The atomic number decreases by 2.

Alpha decay

92U238  2He4 + 90Th234

alpha decay3
These must add up to 238

These must add up to 92

Alpha decay

92U238  2He4 + 90Th234

alpha decay4
Alpha decay

Radon-220 decays by alpha emission. What is the decay product?

84Po216

86Rn220 2He4 + ???

alpha decay5
Alpha decay

Write the alpha decay equations for:

2He4 + 93Np237

2He4 + 82Pb212

2He4 + 86Rn222

  • 95Am241
  • 84Po216
  • 88Ra226 
beta decay
Beta decay

Neutrons are a little more massive than protons; neutrons are neutral.

Beta decay occurs because of the instability of a neutron.

What does this suggest about the composition of neutrons?

beta decay1
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 decay2
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 decay3
Beta decay

0n1 1H1 + -1e0

Decay of a neutron:

neutron

proton

electron

The electron ejected from the nucleus is a beta particle.

beta decay4
Beta decay

0n1  1H1 + -1e0 + 0n0

Technically, the decay of a neutron also involves a neutrino.

neutron

proton

electron

anti-

neutrino

beta decay5
Beta decay

0n1  1H1 + -1e0 + 0n0

Actually, an anti-neutrino.

The word “neutrino” comes from Enrico Fermi, meaning “little neutral one” in Italian.

neutron

proton

electron

anti-

neutrino

beta decay6
Beta decay

0n1  1H1 + -1e0 + 0n0

A neutrino is a particle with no charge and almost no mass.

neutron

proton

electron

anti-

neutrino

beta decay7
Beta decay

0n1  1H1 + -1e0 + 0n0

A neutrino carries off some of the energy in the decay of the neutron.

neutron

proton

electron

anti-

neutrino

beta decay8
Beta decay

0n1  1H1 + -1e0 + 0n0

When predicting the products of beta decay we will ignore neutrinos.

neutron

proton

electron

anti-

neutrino

beta decay9
Start with a

Li atom with

3 protons and

4 neutrons.

Beta decay

Suddenly a

neutron decays!

Now there

are 4 protons and 3 neutrons.

A beta particle goes zipping out of the nucleus.

beta decay10
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 decay11
decay product

beta particle

Beta decay

6C14 7N14 + -1e0

beta decay12
The mass number stays the same.

The atomic number increases by 1.

Beta decay

6C14 7N14 + -1e0

beta decay13
These add up to 14

Notice that these add up to 6

Beta decay

6C14 7N14 + -1e0

beta decay14
Beta decay

Zn-69 decays by beta emission. What is the decay product?

30Zn69 -1e0 + ???

31Ga69

beta decay15
Beta decay

Write the beta decay equations for:

-1e0 + 83Bi214

-1e0 + 28Ni62

  • 82Pb214
  • 27Co62

3. ???  -1e0 + 48Cd113

47Ag113

gamma rays
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 rays1
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
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

did you ever wonder
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.

slide208
Why do they look like this?

Each hair has the same charge.

slide209
Did you ever wonder ...

Because of the electrostatic repulsion…

…the nucleus

shouldn’t even exist!

slide210
Did you ever wonder ...

There must be a force that is stronger than the electrostatic repulsion.

The strong force.

slide211
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.

here s a 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 mystery1
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 mystery2
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

slide216
http://www.chemistry.ccsu.edu/glagovich/teaching/472/ms/instrumentation.html

magnetic

field

Massspectrometer

slide217
http://www.chemistry.ccsu.edu/glagovich/teaching/472/ms/instrumentation.html

magnetic

field

Magnetic field makes charged atoms curve.

here s a mystery3
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 mystery4
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
The solution

What does it tell us?

Recall Einstein’s famous equation:

E = mc2

Matter and energy are equivalent.

the solution1
The solution

Matter can exist as energy and …

… energy can exist as matter.

They are both the same “thing”.

All calculated from E = mc2

the solution2
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 solution3
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 solution4
The solution

The binding energy is the energy required to “take apart” the nucleus to form nothing but individual protons and neutrons.

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 energy1
cancerNuclear 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.

nuclear energy2
Nuclear energy

Forms of ionizing radiation are:

X-rays

Gamma

Beta

Alpha

Cosmic rays

Neutrons

Positrons

Ultraviolet light (UV) can cause cancer, but it is not ionizing radiation.

there s even more
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 fission1
Nuclear fission

Fission – the splitting of an atom after the nucleus absorbs a neutron.

nuclear fission2
Nuclear fission

A neutron collides with a nucleus and is absorbed.

The mass number of the atom increases and the nucleus becomes unstable.

nuclear fission3
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 fission4
Fissionfragment

U-235

U-235

Neutrons

U-235

Fissionfragment

Nuclear fission

Neutron

nuclear fission5
U-235

Neutrons

U-235

Fissionfragment

Nuclear fission

These U-235 atoms can split when hit by neutrons, and release more neutrons, starting a chain reaction.

slide236
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 …

slide237
Detail of ping-pong balls on mousetraps.

http://www.physics.montana.edu/demonstrations/video/modern/demos/mousetrapchainreaction.html

nuclear fission6
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 fission7
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
Containment buildingNuclear reactor

Reactor core

Heat exchanger

Steam generator

Steam to turbine

Fuel rods

Water from cooling lake

Water circulates in the core

nuclear reactor1
Containment building

Cadmium control rods – absorb neutrons

Nuclear reactor

Reactor core

Steam to turbine

Fuel rods

Water from cooling lake

Water circulates in the core

nuclear reactor2
Containment building

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.

Nuclear reactor

Reactor core

Steam to turbine

Fuel rods

Water from cooling lake

Water circulates in the core

nuclear reactor3
Containment building

Water from cooling lake

Nuclear reactor

Reactor core

Fuel rods

Water circulates in the core

nuclear reactor4
Containment buildingNuclear reactor

Reactor core

Heat exchanger

Steam generator

Fuel rods

Water from cooling lake

Water circulates in the core

nuclear reactor5
Containment buildingNuclear reactor

Reactor core

Heat exchanger

Steam generator

Fuel rods

Water from cooling lake

Water circulates in the core

nuclear reactor6
Containment building

Steam to turbine

Nuclear reactor

Reactor core

Heat exchanger

Steam generator

Fuel rods

Water from cooling lake

Water circulates in the core

from nuclear energy to
From nuclear energy to…

Heat exchanger

Steam generator

Transmission wires

turbine

generator

Steam to turbine

Condensed steam

Water from cooling lake

Cooling towers or lake

electrical energy
Electrical energy

Heat exchanger

Steam generator

Transmission wires

turbine

generator

Steam to turbine

Condensed steam

Water from cooling lake

Cooling towers or lake

electrical energy1
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.

Heat exchanger

Steam generator

Transmission wires

turbine

generator

Steam to turbine

Condensed steam

Water from cooling lake

Cooling towers or lake

electrical energy2
Electrical energy

In fact, the only purpose of a nuclear reactor

is to boil water.

pros and cons
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”, …

nuclear fusion
Nuclear fusion

A day without sunshine

is like a day without fusion.

nuclear fusion1
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 fusion2
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 chemistry1
Nuclear Chemistry

Developed by Mike Jones

Pisgah High School

Canton, NC

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