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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


Nuclear chemistry

Atomic

Theory


Nuclear chemistry

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.


Nuclear chemistry

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.


Nuclear chemistry

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We know that parts of Dalton’s atomic theory are no longer valid in today’s modern Quantum Mechanical model of the atom.


Nuclear chemistry

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


Nuclear chemistry

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


Nuclear chemistry

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.


Nuclear chemistry

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.


Nuclear chemistry

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.


Nuclear chemistry

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.


Nuclear chemistry

Alpha scattering

Apparatus for investigating alpha scattering.

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


Nuclear chemistry

+

Alpha scattering

a source

Most of the alpha particles pass through undeflected.


Nuclear chemistry

+

Alpha scattering

a source

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


Nuclear chemistry

+

Alpha scattering

a source

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


Nuclear chemistry

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.


Nuclear chemistry

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


Nuclear chemistry

7 protons

1 proton

2 protons

8 protons

9 protons

9 protons

Ernest Rutherford

We now know…

N + a O + H


Nuclear chemistry

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.


Nuclear chemistry

Radioactivity


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.


Nuclear chemistry

Mass number

protons

+ neutrons

Protons in nucleus

Mass number

Symbol of Element

Atomic number

Mass number /Atomic number

E

A

Z


Nuclear chemistry

Mass number

protons

+ neutrons

Protons in nucleus

Mass number

Symbol of Element

Atomic number

Mass number /Atomic number

U

235

92


Nuclear chemistry

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?


Nuclear chemistry

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?


Nuclear chemistry

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?


Nuclear chemistry

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


Nuclear chemistry

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


Nuclear chemistry

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


Nuclear chemistry

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?


Nuclear chemistry

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.


Nuclear chemistry

Increasing energy

Gamma rays have short wavelengths

… and high energies.


Nuclear chemistry

+ + + + + + + +

Alpha, Beta, Gamma

Electric field from electrically charged plates

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

- - - - - - - - -

Radioactive Source


Nuclear chemistry

+ + + + + + + +

Alpha, Beta, Gamma

Electric field from electrically charged plates

b

g

a

- - - - - - - - -

Radioactive Source


Nuclear chemistry

+ + + + + + + +

Alpha, Beta, Gamma

Electric field from electrically charged plates

b

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

g

a

- - - - - - - - -

Radioactive Source


Nuclear chemistry

Alpha, Beta, Gamma

Paper

Lead

a

Aluminum foil

Radioactive Source


Nuclear chemistry

Alpha, Beta, Gamma

Paper

Lead

b

a

Aluminum foil

Radioactive Source


Nuclear chemistry

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:


Nuclear chemistry

Nuclear Properties Table

Stop!

Complete the chart on notebook paper, then continue.


Nuclear chemistry

Nuclear Properties Table


Nuclear chemistry

Nuclear Properties Table


Nuclear chemistry

Nuclear Properties Table


Nuclear chemistry

Nuclear Properties Table


Nuclear chemistry

Nuclear Properties Table


Nuclear chemistry

Nuclear Properties Table


Nuclear chemistry

Nuclear Properties Table


Nuclear chemistry

Nuclear Properties Table


Nuclear chemistry

Nuclear Properties Table


Nuclear chemistry

Nuclear Properties Table


Protection from radiation

Protection from radiation

  • Shielding2. 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


There are some kinds of radiation you can not protect your self from

There are some kinds of radiation you can not protect your self from.

Radiation


Radiation

Radiation

Gamma rays and high energy cosmic particles from space.

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


Nuclear chemistry

That hazard comes from the uranium beneath your feet.

Uranium in the ground decays according to …


Nuclear chemistry

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


Nuclear chemistry

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.


Nuclear chemistry

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.


Nuclear chemistry

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 ).


Nuclear chemistry

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.


Nuclear chemistry

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.


Nuclear chemistry

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.


Nuclear chemistry

Mass number

protons

+ neutrons

Protons in nucleus

Mass number

Symbol of Element

Atomic number

Mass number /Atomic number

U

235

92


Nuclear chemistry

n

1

0

H

1

1

e

0

-1

Subatomic particles

proton

electron

neutron

What do the numbers represent?


Nuclear chemistry

Fill in the chart with the correct information.


Nuclear chemistry

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.


Nuclear chemistry

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”.


Nuclear chemistry

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.


Nuclear chemistry

Isotopes


Nuclear chemistry

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.


Nuclear chemistry

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.


Nuclear chemistry

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.


Nuclear chemistry

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


Nuclear chemistry

Mass number

Symbol of Element

Atomic number

Symbols for Isotopes

235

U

92

An isotope of uranium


Nuclear chemistry

Mass number

Symbol of Element

Atomic number

Symbols for Isotopes

This form solves the word processor dilemma.

U

235

92

An isotope of uranium


Nuclear chemistry

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?


Nuclear chemistry

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.


Nuclear chemistry

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


Nuclear chemistry

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


Nuclear chemistry

Finding the number of Protons, Neutrons, and Electrons

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


Nuclear chemistry

Finding the number of Protons, Neutrons, and Electrons


Nuclear chemistry

Finding the number of Protons, Neutrons, and Electrons

Stop!

Complete the table, then go on.


Nuclear chemistry

Finding the number of Protons, Neutrons, and Electrons


Nuclear chemistry

Finding the number of Protons, Neutrons, and Electrons


Nuclear chemistry

Finding the number of Protons, Neutrons, and Electrons


Nuclear chemistry

Finding the number of Protons, Neutrons, and Electrons


Nuclear chemistry

Finding the number of Protons, Neutrons, and Electrons


Nuclear chemistry

Finding the number of Protons, Neutrons, and Electrons


Nuclear chemistry

Finding the number of Protons, Neutrons, and Electrons


Nuclear chemistry

Atomic mass is the weighted average of all the isotopes of an element

Boron has two isotopes:

B-1019.8%10.01 amu

B-1180.2%11.01 amu

0.198 x 10.01 + 0.802 x 11.01 =

10.81 amu


Nuclear chemistry

Atomic mass is the weighted average of all the isotopes of an element

Determine the atomic mass of silicon:

Si-2892.23%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


Nuclear chemistry

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.


Nuclear chemistry

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 - 3575.85%34.97 amu

Cl - 3724.15%36.97 amu

The average atomic mass is 35.453 amu.


Nuclear chemistry

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-2090%

Ne-2210%


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.


Nuclear chemistry

How did knowing about Graham’s Law allow the United States to win World War II?


Nuclear chemistry

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

Fat Man, and …

Little Boy

Atomic bombs dropped on Hiroshima and Nagasaki


Nuclear chemistry

Hiroshima


Nuclear chemistry

Nagasaki


Nuclear chemistry

Manhattan Project

Oak Ridge, TN

Graham’s law

Gaseous diffusion

Enriched uranium


Nuclear chemistry

Manhattan Project


Nuclear chemistry

Manhattan Project

Naturally occurring uranium is mostly U-238

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


Nuclear chemistry

Manhattan Project

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

Bomb grade uranium is over 90% U-235


Nuclear chemistry

Manhattan Project

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

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


Nuclear chemistry

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.


Nuclear chemistry

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.


Nuclear chemistry

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.


Nuclear chemistry

Manhattan Project

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


Nuclear chemistry

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.


Nuclear chemistry

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.


Half life

Half life


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


Decay equations

Decay equations


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


What holds the nucleus together

What holds the nucleus together?


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.


Nuclear chemistry

Why do they look like this?

Each hair has the same charge.


Nuclear chemistry

Did you ever wonder ...

Because of the electrostatic repulsion…

…the nucleus

shouldn’t even exist!


Nuclear chemistry

Did you ever wonder ...

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

The strong force.


Nuclear chemistry

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

There is a closely related mystery.


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


Nuclear chemistry

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

magnetic

field

Massspectrometer


Nuclear chemistry

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.


Is this binding energy related to nuclear energy

Is this binding energy related to nuclear energy?


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

cancer

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.


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 fission

Nuclear Fission


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.


Nuclear chemistry

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 …


Nuclear chemistry

Detail of ping-pong balls on mousetraps.

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


Nuclear chemistry

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 chemistry

Nuclear reactor


Nuclear chemistry

Nuclear reactor


Nuclear reactor

Containment building

Nuclear 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 building

Nuclear reactor

Reactor core

Heat exchanger

Steam generator

Fuel rods

Water from cooling lake

Water circulates in the core


Nuclear reactor5

Containment building

Nuclear 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”, …


What about fusion

What about fusion?


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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