Nuclear Chemistry Last revision: 110409 M. Jones Pisgah High School.

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Transcript of Nuclear Chemistry Last revision: 110409 M. Jones Pisgah High School.

Nuclear Chemistry

Last revision: 110409

M. Jones

Pisgah High School

Atomic Theory

Atomic Theory

Atoms are the smallest particles of elements.

Atoms were first proposed by Democritus over 2000 years ago.

The idea of atoms was reintroduced in 1803 by John Dalton.

1. Atoms are tiny, discrete particles 2. Atoms are indestructible3. Atoms of the same element have the

same mass and properties4. Atoms combine in simple whole-

number ratios5. Atoms in different ratios produce

different compounds.

Dalton’s Atomic Theory

1. Atoms are tiny, discrete particles 2. Atoms are indestructible3. Atoms of the same element have the

same mass and properties4. Atoms combine in simple whole-

number ratios5. Atoms in different ratios produce

different compounds.

We know that parts of Dalton’s atomic theory are no longer valid in today’s modern Quantum Mechanical model of the atom.

Dalton’s Atomic Theory

1. Atoms are tiny, discrete particles 2. Atoms are indestructible3. Atoms of the same element have the

same mass and properties

We know that atoms are made up of smaller particles, and that there are slight differences between atoms of the same element - isotopes.

Dalton’s Atomic Theory

Atomic Theory

We know that atoms are made up of protons, neutrons and electrons.

Protons and neutrons are located in a small, dense, positively charged nucleus.

We know that atoms are mostly empty space.

Atomic Theory

In 1897 J. J. Thomson discovered that cathode rays were actually streams of subatomic particles.

These particles carried a negative charge and were called electrons.

Cathode ray tube

Atomic Theory

We know atoms are mostly empty space and that protons and neutrons

are located in a small, dense, positively charged nucleus because of Rutherford’s explanation of the

alpha scattering (gold foil) experiment.

+Most of the alpha particles pass through undeflected.

Atomic Theory source

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

Atomic Theory source

Atomic Theory

We know that electrons are outside the nucleus in an “electron cloud”.

Electrons exist in specific energy levels, which explains the line

spectra of the elements.

Started with the Bohr model.

Atomic Theory

We now use the Quantum Mechanical Model of the atom.

Quantum Theory describes the nature of electrons and their

interactions with the electrons of other atoms in chemical reactions.

Atomic Theory

The subatomic particles that make up atoms have known properties like mass and electrical charge.

Our understanding came through the efforts of a number of

scientists like Thomson, Millikan, Rutherford, and Chadwick.

Property Proton Neutron Electron

Symbols

Location

Rel. mass

Mass (amu)

Mass (g)

Rel. charge

Charge (C)

Fill in the chart with the correct information.

Property Proton Neutron Electron

Symbols p+ and 1H1 n0 and 0n

1 e- and -1e0

Location

Rel. mass

Mass (amu)

Mass (g)

Rel. charge

Charge (C)

Property Proton Neutron Electron

Symbols p+ and 1H1 n0 and 0n

1 e- and -1e0

Location nucleus nucleus cloud outside nucleus

Rel. mass

Mass (amu)

Mass (g)

Rel. charge

Charge (C)

Property Proton Neutron Electron

Symbols p+ and 1H1 n0 and 0n

1 e- and -1e0

Location nucleus nucleus cloud outside nucleus

Rel. mass 1 1 1/1837

Mass (amu)

Mass (g)

Rel. charge

Charge (C)

Property Proton Neutron Electron

Symbols p+ and 1H1 n0 and 0n

1 e- and -1e0

Location nucleus nucleus cloud outside nucleus

Rel. mass 1 1 1/1837

Mass (amu) 1.0073 amu 1.0087 amu 0.00549 amu

Mass (g)

Rel. charge

Charge (C)

Property Proton Neutron Electron

Symbols p+ and 1H1 n0 and 0n

1 e- and -1e0

Location nucleus nucleus cloud outside nucleus

Rel. mass 1 1 1/1837

Mass (amu) 1.0073 amu 1.0087 amu 0.00549 amu

Mass (g) 1.673x10-24 1.675x10-24 9.11x10-29

Rel. charge

Charge (C)

Property Proton Neutron Electron

Symbols p+ and 1H1 n0 and 0n

1 e- and -1e0

Location nucleus nucleus cloud outside nucleus

Rel. mass 1 1 1/1837

Mass (amu) 1.0073 amu 1.0087 amu 0.00549 amu

Mass (g) 1.673x10-24 1.675x10-24 9.11x10-29

Rel. charge +1 0 -1

Charge (C)

Property Proton Neutron Electron

Symbols p+ and 1H1 n0 and 0n

1 e- and -1e0

Location nucleus nucleus cloud outside nucleus

Rel. mass 1 1 1/1837

Mass (amu) 1.0073 amu 1.0087 amu 0.00549 amu

Mass (g) 1.673x10-24 1.675x10-24 9.11x10-29

Rel. charge +1 0 -1

Charge (C) +1.6x10-19 C 0 -1.6x10-19 C

Subatomic particles - Summary1. Protons and neutrons are located in

the nucleus.2. Protons and neutrons have almost

the same mass. Neutrons heavier.3. Electrons are outside the nucleus and

much lighter than proton or neutron.4. Protons and electrons have the same

charge but opposite polarity. 5. Neutrons have no charge.

Isotopes

Isotopes …

Therefore, isotopes of the same element have different masses.

…of the same element have the same number of protons and electrons but different numbers of neutrons.

Isotopes …

…don’t have to be radioactive. Some isotopes are unstable and

decay, releasing alpha or beta particles, or gamma rays.

But, there are many stable isotopes that don’t decay.

Isotopes …

Mass number - the sum of the protons and neutrons in the nucleus.

Atomic number - the number of protons in the nucleus of an atom.

…have different mass numbers but the same atomic number.

Symbols for Isotopes

EA

Z

Symbol of Element

Mass number

Atomic number

A is the symbol for mass number

Z is the symbol for atomic number

U235

92

Symbols for Isotopes

Symbol of Element

Mass number

Atomic number

An isotope of uranium

Symbols for Isotopes

U235

92

Mass number

Symbol of Element

Atomic number

An isotope of uranium

This form solves the word processor dilemma.

U-235

Symbol of Element

Mass number

How do you know the atomic number?

Find U in the periodic table.

Symbols for Isotopes

Z = 92

Some elements have several Isotopes

Lead has four naturally occurring isotopes, Pb-204, Pb-206, Pb-207, and Pb-208; but there are 23 man-made isotopes of lead.

Some elements have several Isotopes

Bismuth has only one naturally occurring isotope,

Bi-209, but there are 22 man-made isotopes of bismuth.

Finding the number of Protons, Neutrons, and Electrons

The number of electrons in a neutral atom equals the

number of protons.

The atomic number is the number of protons in the nucleus.

neutrons = A - Z

The number of neutrons is the difference between the mass number and the atomic number.

Finding the number of Protons, Neutrons, and Electrons

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

U-235

A = 235protons + neutrons = 235

Z = 92protons = 92electrons = 92

Finding the number of Protons, Neutrons, and Electrons

U-235

A = 235protons + neutrons = 235

Z = 92protons = 92electrons = 92

Finding the number of Protons, Neutrons, and Electrons

How many neutrons are in a U-235 atom?

U-235

235 – 92 = 143 neutrons

Z = 92protons = 92electrons = 92

Finding the number of Protons, Neutrons, and Electrons

How many neutrons are in a U-235 atom?

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

A. In the Ba-137 isotope …… Z = 56 and A = 137137 – 56 = 81 neutrons

Finding the number of Protons, Neutrons, and Electrons

Copy the following table on notebook paper, and

fill in the blanks.

Finding the number of Protons, Neutrons, and Electrons

Element Symbol Z A #p #n #e

Zinc 66

In 68

85 38

82 210

Rn 136

35 47

Finding the number of Protons, Neutrons, and Electrons

Element Symbol Z A #p #n #e

Zinc 66

In 68

85 38

82 210

Rn 136

35 47

Stop!Complete the table, then go

on.

Finding the number of Protons, Neutrons, and Electrons

Element Symbol Z A #p #n #e

Zinc 66

In 68

85 38

82 210

Rn 136

35 47

Finding the number of Protons, Neutrons, and Electrons

Element Symbol Z A #p #n #e

Zinc Zn 30 66 30 36 30

In 68

85 38

82 210

Rn 136

35 47

Finding the number of Protons, Neutrons, and Electrons

Element Symbol Z A #p #n #e

Zinc Zn 30 66 30 36 30

Indium In 49 117 49 68 49

85 38

82 210

Rn 136

35 47

Finding the number of Protons, Neutrons, and Electrons

Element Symbol Z A #p #n #e

Zinc Zn 30 66 30 36 30

Indium In 49 117 49 68 49

Strontium Sr 38 85 38 47 38

82 210

Rn 136

35 47

Finding the number of Protons, Neutrons, and Electrons

Element Symbol Z A #p #n #e

Zinc Zn 30 66 30 36 30

Indium In 49 117 49 68 49

Strontium Sr 38 85 38 47 38

Lead Pb 82 210 82 128 82

Rn 136

35 47

Finding the number of Protons, Neutrons, and Electrons

Element Symbol Z A #p #n #e

Zinc Zn 30 66 30 36 30

Indium In 49 117 49 68 49

Strontium Sr 38 85 38 47 38

Lead Pb 82 210 82 128 82

Radon Rn 86 222 86 136 86

35 47

Finding the number of Protons, Neutrons, and Electrons

Element Symbol Z A #p #n #e

Zinc Zn 30 66 30 36 30

Indium In 49 117 49 68 49

Strontium Sr 38 85 38 47 38

Lead Pb 82 210 82 128 82

Radon Rn 86 222 86 136 86

Bromine Br 35 82 35 47 35

Finding the number of Protons, Neutrons, and Electrons

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

element

Boron has two isotopes:B-10 19.8% 10.01 amuB-11 80.2% 11.01 amu

0.198 x 10.01 + 0.802 x 11.01 = 10.81 amu

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

element

Determine the atomic mass of silicon:Si-28 92.23% 27.977 amuSi-29 4.67% 28.976 amuSi-30 3.10% 29.974 amu

0.9223 x 27.977 + 0.0467 x 28.976 + 0.0310 x 29.974 = 28.086 amu

Consider the two isotopes of chlorine. Which isotope is more abundant?Cl - 35 ??.?? % 34.97 amuCl - 37 ??.?? % 36.97 amu

The average atomic mass is 35.453 amu.

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

element

Consider the two isotopes of chlorine. Which isotope is more abundant?Cl - 35 75.85% 34.97 amuCl - 37 24.15% 36.97 amu

The average atomic mass is 35.453 amu.

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

element

Which isotope of neon is more abundant? Ne-20 or Ne-22

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

element

Ne-20 90%Ne-22 10%

How are isotopes of the same element alike and different?

Alike:

1. Number of protons and electrons

2. Atomic number

3. Chemical properties

Different:

1. Number of neutrons

2. Mass Number

3. Atomic mass of the isotopes

Which of the following is the same for the three isotopes of magnesium?

1. The atomic number of 122. The number of protons and electrons3. The number of neutrons4. The atomic weight of 24.986 AMU5. The reaction with hydrochloric acid6. The speed of gaseous Mg atoms

1. The atomic number of 12

All three isotopes of magnesium have the same atomic number.

Same

Which of the following is the same for the three isotopes of magnesium?

2. The number of protons and electrons

All isotopes of the same element have the same number of protons in the nucleus, and electrons outside the nucleus.

Same

Which of the following is the same for the three isotopes of magnesium?

3. The number of neutrons

The number of neutrons varies with the isotope. Different isotopes have different numbers of neutrons.

Not the same

Which of the following is the same for the three isotopes of magnesium?

4. Atomic weight of 24.986 AMU

Mg-24 23.985 AMU

Mg-25 24.986 AMU

Mg-26 25.983 AMU

Not the same

Which of the following is the same for the three isotopes of magnesium?

5. The reaction with HCl

All isotopes of the same element react the same chemically.

Same

The number and arrangement of electrons is the same for each isotope.

Which of the following is the same for the three isotopes of magnesium?

6. The speed of gaseous Mg atoms

The speeds of atoms depend on mass.

Heavier atoms move more slowly, and lighter atoms move faster.

Not the same

Which of the following is the same for the three isotopes of magnesium?

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

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

Fat Man, and … Little Boy

Atomic bombs dropped on Hiroshima and Nagasaki

Hiroshima

Nagasaki

Manhattan Project

Oak Ridge, TN

Gaseous diffusion

Graham’s law

Enriched uranium

Manhattan Project

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

Manhattan Project

Naturally occurring uranium is mostly U-238

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

Manhattan Project

Bomb grade uranium is over 90% U-235

The process of increasing the percentage of U-235 is

called enrichment.

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

Manhattan Project

Uranium ore is reacted with fluorine to make gaseous UF6.

Then the gaseous UF6 is introduced into chambers with porous disks in the ends.

Manhattan Project

The lighter UF6 molecules containing U-235 effuse

through the holes in the disk faster. There is more U-235

on the other side of disk.

Manhattan Project

As the UF6 continues to move through many, many disks, the percentage of U-235 atoms in the gas increases, resulting in

enrichment.

Manhattan Project

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

Manhattan Project

1

2

2

1

r

r

M

M

The enriched UF6 containing a much higher percentage of U-235 atoms, is reacted with water to make uranium oxide and HF. The uranium oxide is dried and made into fuel pellets.

Manhattan Project

Uranium Pellet

Fuel rod assembly

Only one element has unique names for its isotopes …

tritium H

deuterium H

hydrogen H

31

21

11

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

Some isotopes are radioactive

Radioactive isotopes are called radioisotopes.

Radioisotopes can emit alpha, beta or gamma

radiation as they decay.

Man-made Isotopes

Cobalt-59 occurs naturally. When a neutron “sticks” to the nucleus,

cobalt-60 is formed.

Man-made isotopes are usually made by bombarding atoms with protons or neutrons.

Uses for Isotopes

Radioisotopes are used as tracers in chemical reactions.

Radioisotopes are used in “imaging” living and nonliving systems.

Radioisotopes are used to kill cancer cells. (Co-60, Bi-212)

Demonstrations with radioactivity

Recall what you have discovered about nuclear radiation.

Mica window (fragile)

Wire (+ side of circuit)Metal shield (- side)Low pressure Ar gas

Counter 2435

Geiger-Mueller Tube

GM Tube

Rays leave the sourceSome hit the GM tube

Most do nothing

One ray may cause a discharge…

Source and the detector clicks

GM TubeFilled with low pressure argon gas

About 1% efficiency

About 1 in 100 rays causes an electric spark between the case and the wire

Each spark registers as a count or click on the counter

Properties of alpha, beta and gamma

radiation

Subatomic particles

H1

1 e0

-1

n10proton

neutronelectron

What do the numbers represent?

Mass number /Atomic number

U235

92

Mass number

Symbol of Element

Atomic number

protons + neutrons

Protons in nucleus

Mass number

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

What is the atomic number

of an particle?2 He4

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

How many times heavier is an alpha particle than

a hydrogen atom?4

Beta () particles are high speed electrons ejected from the nuclei of atoms and have the symbol -1e0.What is the mass number of a particle?

-1e0

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

No protons or neutrons in an electron. -1e0

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

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

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

LocationLocationLocation

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

Gamma () rays are high energy electromagnetic waves, not particles.

No protons, neutrons or electrons.

Gamma rays have short wavelengths and high energies and travel at the speed of light.

Gamma rays have short wavelengths

… and high energies.

Increasing energy

Alpha, Beta, Gamma

Radioactive Source

- - - - - - - - -

+ + + + + + + +

Electric field from electrically charged plates

What is the effect of an electric field on

Alpha, Beta, Gamma

Radioactive Source

- - - - - - - - -

+ + + + + + + +

Electric field from electrically charged plates

Alpha, Beta, Gamma

Radioactive Source

- - - - - - - - -

+ + + + + + + +

Are , and rays deflected by magnetic fields?

Electric field from electrically charged plates

Radioactive Source

Paper

Aluminum foil

Lead

Alpha, Beta, Gamma

Radioactive Source

Paper

Aluminum foil

Lead

Alpha, Beta, Gamma

Radioactive Source

Paper

Aluminum foil

Lead

Alpha, Beta, Gamma

Radiation Project

Create a table listing information for each of the three kinds of radiation:

Alpha, beta and gamma

Properties to include in your table:

(1) Greek letter

(2) symbol

(3) actually is

(4) atomic number

(5) mass number

(6) relative mass

(7) relative. charge

(8) penetrating ability

(9) shielding

Nuclear Properties TableProperty Alpha Beta Gamma

Greek Letter

Symbol

Actually is…

Atomic number

Mass number

Relative mass

Relative charge

Penetrating

Shielding

Stop!Complete the chart on notebook paper,

then continue.

Nuclear Properties TableProperty Alpha Beta Gamma

Greek Letter

Symbol

Actually is…

Atomic number

Mass number

Relative mass

Relative charge

Penetrating

Shielding

Nuclear Properties TableProperty Alpha Beta Gamma

Greek Letter Symbol

Actually is…

Atomic number

Mass number

Relative mass

Relative charge

Penetrating

Shielding

Nuclear Properties TableProperty Alpha Beta Gamma

Greek Letter Symbol

2He4-1e0 NA

Actually is…

Atomic number

Mass number

Relative mass

Relative charge

Penetrating

Shielding

Nuclear Properties TableProperty Alpha Beta Gamma

Greek Letter Symbol

2He4-1e0 NA

Actually is… He nucleus electron EM energy

Atomic number

Mass number

Relative mass

Relative charge

Penetrating

Shielding

Nuclear Properties TableProperty Alpha Beta Gamma

Greek Letter Symbol

2He4-1e0 NA

Actually is… He nucleus electron EM energy

Atomic number 2 -1 NA

Mass number

Relative mass

Relative charge

Penetrating

Shielding

Nuclear Properties TableProperty Alpha Beta Gamma

Greek Letter Symbol

2He4-1e0 NA

Actually is… He nucleus electron EM energy

Atomic number 2 -1 NA

Mass number 4 0 NA

Relative mass

Relative charge

Penetrating

Shielding

Nuclear Properties TableProperty Alpha Beta Gamma

Greek Letter Symbol

2He4-1e0 NA

Actually is… He nucleus electron EM energy

Atomic number 2 -1 NA

Mass number 4 0 NA

Relative mass 4 1/1837NA

Relative charge

Penetrating

Shielding

Nuclear Properties TableProperty Alpha Beta Gamma

Greek Letter Symbol

2He4-1e0 NA

Actually is… He nucleus electron EM energy

Atomic number 2 -1 NA

Mass number 4 0 NA

Relative mass 4 1/1837NA

Relative charge +2 -1 NA

Penetrating

Shielding

Nuclear Properties TableProperty Alpha Beta Gamma

Greek Letter Symbol

2He4-1e0 NA

Actually is… He nucleus electron EM energy

Atomic number 2 -1 NA

Mass number 4 0 NA

Relative mass 4 1/1837NA

Relative charge +2 -1 NA

Penetrating Low Medium High

Shielding

Nuclear Properties TableProperty Alpha Beta Gamma

Greek Letter Symbol

2He4-1e0 NA

Actually is… He nucleus electron EM energy

Atomic number 2 -1 NA

Mass number 4 0 NA

Relative mass 4 1/1837NA

Relative charge +2 -1 NA

Penetrating Low Medium High

Shielding 2.5 cm of air;anything else

Metal, plastic or wood

Lead or concrete

Protection from radiation1. Shielding 2. Distance

How do you protect yourself from …

Alpha

Beta

Gamma

2.5 cm of air, paper, skinaluminum, lead, other metals, wood, plastic, etc.up to a foot or two of lead, many feet of concrete

There are some kinds of radiation you can not

protect your self from.

Gamma rays and high energy cosmic particles from space.

But there is one kind of radiation hazard that you

can protect against.

Radiation

That hazard comes from the uranium beneath your feet.

Uranium in the ground decays according to …

Uranium-238 decays through

many steps to make stable

lead-206

The uranium decay series

http://library.tedankara.k12.tr/chemistry/vol1/nucchem/trans90.htm

The uranium decay series

Radon is the only gas in the series.

http://library.tedankara.k12.tr/chemistry/vol1/nucchem/trans90.htm

Hazards from radon

Since radon is the only gas in the decay series of uranium …

…it can work its way up through the ground and into your

basements and crawl spaces.

You breathe radon into your lungs.

Hazards from radon

And when radon is in your lungs…

…it can decay and release an alpha particle …

…which travels only a short distance before it is absorbed by your lungs, and transfers its energy.

Hazards from radon

This ionizing radiation in your lungs can cause lung cancer.

Smoking cigarettes and breathing radon really increases your

chances of getting lung cancer.

Protecting against radon

Get a test kit to see if there is a problem. Charcoal canisters, which are sent off for analysis.

Abatement:Seal places where gas gets in.

Ventilation – bring in fresh air.

Half life

What is half life?

Half life is the time needed for one half of a radioisotope to decay.

Suppose you start with 100.0 grams of a radioisotope that has a half life

of exactly 1 year.

What is half life?

How much will be left after 1 year?

Suppose you start with 100.0 grams of a radioisotope that has a half life

of exactly 1 year.

What is half life?

After one year there will be 50.0 g left.

Suppose you start with 100.0 grams of a radioisotope that has a half life

of exactly 1 year.

After a second year there will be 25.0 g left.

What is half life?

After a third year there will be 12.5 grams left.

After one year there will be 50.0 g left. After a second year there will be

25.0 g left.

After a fourth year there will be 6.25 grams left.

Half life project1. Pick a mass between 10g and 50g. 2. Decide on a half life – any time.3. Scale your graph – mass on y-axis

and at least six (6) half-lives on the x-axis.

4. Plot the masses after intervals of one half-life.

Half life project5. What shape is the graph?6. When will the mass of the

radioisotope fall to zero?7. When is the radioactivity no

longer a problem? 8. What mathematical function

describes radioactive decay?

Half life projectm

ass

time

10

52.5

t1/2 t1/2

Half life projectm

ass

time

2.5

t1/2 t1/2

10

5

Half life projectA

ctiv

ity

(cou

nts/

min

)

Time (min)

200

10050

t1/2 t1/2

Exponential decay

A = A0e-kt

Half life project

Time (min)

10050

t1/2 t1/2A

ctiv

ity

(cou

nts/

min

)

background

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

200

Half life projectQuestions:

1. A radioisotope has a half-life of 100 years. How long will it take for the radiation to decrease to 1/16 of its original value?

400 years

Half life projectQuestions:

2. A radioisotope has an activity of 560 counts per minute. After 16 hours the count rate has dropped to 35 counts per minute. What is the half life of the radioisotope?

4 hours

Decay equations

Alpha decay

In alpha decay, an alpha particle (2He4) is released from the nucleus.

The alpha particle carries away two protons and two neutrons.

Alpha decay

92U238 2He4 + 90Th234

alpha particle

decay product

Alpha decay

92U238 2He4 + 90Th234

The atomic number decreases by 2.

The mass number decreases by 4.

Alpha decay

These must add up to 238

These must add up to 92

92U238 2He4 + 90Th234

Alpha decay

86Rn220 2He4 + ???

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

84Po216

Alpha decay

Write the alpha decay equations for:

1. 95Am241

2. 84Po216

3. 88Ra226

2He4 + 93Np237

2He4 + 82Pb212

2He4 + 86Rn222

Beta decay

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

What does this suggest about the composition of neutrons?

Beta decay occurs because of the instability of a neutron.

Beta decayScientists used to think that neutrons might be a combination of a proton and an electron.

We know that neutrons decay into protons, which stay in the nucleus,

and electrons, which are ejected from the nucleus as beta particles.

Beta decay

0n1 1H1 + -1e0

neutron proton electron

The electron ejected from the nucleus is a beta particle.

Decay of a neutron:

Beta decay

0n1 1H1 + -1e0 + 00

neutron proton electron

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

anti-neutrino

Beta decay

0n1 1H1 + -1e0 + 00

neutron proton electron

Actually, an anti-neutrino.

anti-neutrino

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

Beta decay

0n1 1H1 + -1e0 + 00

neutron proton electron

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

anti-neutrino

Beta decay

0n1 1H1 + -1e0 + 00

neutron proton electron

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

anti-neutrino

Beta decay

0n1 1H1 + -1e0 + 00

neutron proton electron

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

anti-neutrino

Beta decayStart with a Li atom with

3 protons and 4 neutrons.

Suddenly a neutron decays!

Now there are 4 protons

and 3 neutrons.

A beta particle goes zipping out of

the nucleus.

Beta decay

The number of neutrons

The number of protons

The mass number

The atomic number

A neutron decays to make a proton.

decreases by 1

increases by 1

stays the same.

increases by 1

Beta decay

6C14 7N14 + -1e0

beta particle

decay product

Beta decay

6C14 7N14 + -1e0

The atomic number increases by 1.

The mass number stays the same.

Beta decay

6C14 7N14 + -1e0

Notice that these add up to 6

These add up to 14

Beta decay

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

30Zn69 -1e0 + ??? 31Ga69

Beta decay

Write the beta decay equations for:

1. 82Pb214

2. 27Co62

-1e0 + 83Bi214

-1e0 + 28Ni62

3. ??? -1e0 + 48Cd11347Ag113

Review: decay equationsAlpha:

Go down two on periodic tableAtomic number decreases by 2Mass number decreases by 4

Beta:Go up one on periodic tableAtomic number increases by 1Mass number stays the same

Nuclear energy

All have enough energy to ionize atoms.

Gamma rays are electromagnetic energy.

Alpha and beta particles have high kinetic energies.

All nuclear decay is accompanied by a release of energy.

Nuclear energy

This can result in damage to your body.

Ionization occurs when electrons are removed from

atoms by or radiation.

An ion is a “charged atom” or group of atoms.

cancer

Nuclear energy

Forms of ionizing radiation are:

Alpha Beta Gamma X-rays

Cosmic rays

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

Neutrons Positrons

There’s even more!

But there is an even greater release of energy when the atom splits apart …

Some of the energy that holds the nucleus together is carried away by the alpha, beta and gamma radiation.

Nuclear Fission

Nuclear fission

Fission – the splitting of an atom after being struck by a neutron.

Nuclear fission

The neutrons strike other atoms causing more fission.

Plus, two or three neutrons are released along with a great deal of energy.

The atom splits into two or more fission fragments.

U-235U-235

U-235

Nuclear fission

NeutronNeutrons

Fission fragment

Fission fragment

Nuclear fission

U-235

U-235

Neutrons

Fission fragment

These U-235 atoms can split when hit by neutrons, and

release more neutrons, starting a

chain reaction.

Nuclear fission

To picture a chain reaction, imagine 50 mousetraps in a wire cage.

And on each mousetrap are two ping-pong balls.

Now imagine dropping one more ping-pong ball into the cage …

Detail of ping-pong balls on mousetraps.

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

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

Nuclear fission

Billions of splitting atoms releases a huge amount of heat energy.

This energy originally held the nucleus together.

As the chain reaction proceeds, energy is released as heat energy.

Nuclear fission

This heat energy can be harnessed to boil water, creating steam,

that can spin a turbine,

that can turn a generator,

creating electricity.

Nuclear reactor

Nuclear reactor

Nuclear reactorReactor core

Containment building

Fue

l rod

s

Heat exchangerSteam generator

Water circulates in the core

Steam to turbine

Water from cooling lake

Water from cooling lake

Nuclear reactorReactor core

Containment building

Fue

l rod

s

Water circulates in the core

Steam to turbine

Cadmium control rods – absorb neutrons

Water from cooling lake

Nuclear reactorReactor core

Fue

l rod

s

Water circulates in the core

Steam to turbine

The water in the core serves two functions.

(1) The water cools the core and carries away heat.

(2) Water is a moderator. The water slows the

neutrons so that they can cause fission. Fast

neutrons do not cause fission.

Containment building

Nuclear reactorReactor core

Containment building

Fue

l rod

s

Water circulates in the core

Water from cooling lake

Nuclear reactorReactor core

Containment building

Fue

l rod

s

Water circulates in the core

Water from cooling lake

Heat exchangerSteam generator

Nuclear reactorReactor core

Containment building

Fue

l rod

s

Water circulates in the core

Water from cooling lake

Heat exchangerSteam generator

Nuclear reactorReactor core

Containment building

Fue

l rod

s

Water circulates in the core

Water from cooling lake

Steam to turbine

Heat exchangerSteam generator

From nuclear energy to…

Steam to turbine

Water from cooling lake Cooling towers

or lake

turbine generator

Transmission wires

Condensed steam

Heat exchangerSteam generator

Steam to turbine

Water from cooling lake Cooling towers

or lake

turbine generator

Transmission wires

Condensed steam

Heat exchangerSteam generator

Electrical energy

Steam to turbine

Water from cooling lake Cooling towers

or lake

turbine generator

Transmission wires

Condensed steam

Heat exchangerSteam generator

Electrical energy

This part of the system is the same regardless of how the steam is produced. The heat can come from nuclear energy or by burning coal, natural gas or fuel oil.

Electrical energy

In fact, the only purpose of a nuclear reactor is to boil water.

Pros and cons

Cheap, plentiful power, no CO2, nuclear waste, terrorist attack, running out of oil and coal, on-site storage, breeder reactors, transportation of spent fuel, “not in my backyard”, …

What about fusion?

Nuclear fusion

is like a day without fusion.

A day without sunshine

Nuclear fusion

Is nuclear fusion an alternative to fission for producing electricity?

Fusion occurs when hydrogen atoms combine to make helium,

and release energy.

Nuclear fusion powers the sun.

Nuclear fusion

Now consumes more energy than it releases.

Magnetic bottle. Control problems.

Occurs at very high temperatures which nothing can withstand.

Fusion not now technically feasible.

Nuclear Chemistry

Developed by Mike JonesPisgah High School

Canton, NC