Intro to Nuclear Chemistry

http://www.chem.orst.edu/graduate/pics/Reactor.jpgPowerPoint basics from Mrs. Coyle and other Internet Sources

Learning Objectives

• TLW understand the basic process of nuclear chemistry (TEKS 12)– TLW be able to describe alpha, beta, and

gamma radiation (TEKS 12.A)– TLW describe radioactive decay process in

terms of balanced nuclear equations (TEKS 12.B)

– TLW compare fission and fusion reactions (TEKS 12.C)

Anticipatory Exercise

• Background Radiation – What’s YOUR Exposure?– Flinn Scientific ChemTopicTM Labs – Book 18,

page 2

How does a nuclear reactor work?

http://www.lanl.gov/science/1663/images/reactor.jpg

How does a small mass contained in this bomb cause……

• Nuclear Bomb of 1945 known as “fat man”

http://www.travisairmuseum.org/assets/images/fatman.jpg

…this huge nuclear explosion?

http://library.thinkquest.org/06aug/01200/Graphics/705px-Nuclear_fireball.jpg

Is there radon in your basement?

http://a.abcnews.com/images/Blotter/abc_1radon_ad_070625_ssh.jpg

Nuclear Notation

Practice Using Nuclear Notation

• How would you write the following elements using nuclear notation?

H

C

Co

U

Nucleons

• Protons and Neutrons

• The nucleons are bound together by the strong force.

Isotopes

• Atoms of a given element with:

same #protons

but

different # neutrons

H H H

http://education.jlab.org/glossary/isotope.html

Isotopes of Carbon

• Isotopes of certain unstable elements that spontaneously emit particles and energy from the nucleus.

• Henri Beckerel 1896 accidentally observed radioactivity of uranium salts that were fogging photographic film.

• His associates were Marie and Pierre Curie.

Radioactive Isotopes

Marie Curie: 1867 - 1934, in Poland as Maria Sklodowska

• Lived in France

• 1898 discovered the elements polonium and radium.

http://www.radiochemistry.org/nuclearmedicine/pioneers/images/mariecurie.jpg

Marie Curie a Pioneer of Radioactivity

• Winner of 1903 Nobel Prize for Physics with Henri Becquerel and her husband, Pierre Curie (1859 – 1906)

• Winner of the sole 1911 Nobel Prize for Chemistry

• Sadly, she and Pierre died of radiation poisoning

General Nuclear Equations

• Handout of Graphic Organizer on General Nuclear Equations

3 Main Types of Radioactive Decay

• Alpha

• Beta

• Gamma

Emission of alpha particles :

• helium nuclei • two protons and two neutrons • charge +2e  • can travel a few inches through air• can be stopped by a sheet of

paper, clothing.

Alpha Decay

Alpha Decay

Uranium Thorium alpha particle

Alpha Decay

http://education.jlab.org/glossary/alphadecay.gif

Beta Decay

• Beta particles : electrons ejected from the nucleus when neutrons decay

( no p+ +- )

• Beta particles have the same charge and mass as "normal" electrons.

Beta Decay

• Beta particles : electrons ejected from the nucleus when neutrons decay

no p+ +-

• Beta particles have the same charge and

mass as "normal" electrons.

• Can be stopped by aluminum foil or a block of wood.

Beta Decay

Beta Decay

Thorium Protactinium beta particle

• Gamma radiation electromagnetic energy that is released. 

• Gamma rays are electromagnetic waves.

• They have no mass.• Gamma radiation has no charge.

– Most Penetrating, can be stopped by 1 m thick concrete or a several cm thick sheet of lead.

Gamma Decay

Examples of Radioactive DecayAlpha Decay

Po Pb + He

Beta Decay p n + e

n p + e

C N + e

Gamma Decay

Ni Ni + (excited nucleus)

Which is more penetrating & potentially more harmful? Why?

Second Graphic Organizer

• Nuclear Decay Organizer (pdf) - link

Part II

•Balancing Nuclear Equations

Balancing Nuclear ReactionsBalancing Nuclear Reactions•In the reactants (starting materials – on the left side of an equation) and products (final products – on the right side of an equation) – Law of Conservation of Mass

Atomic numbers must balanceand

Mass numbers must balance

•Use a particle or isotope to fill in the missing protons and neutrons

Nuclear ReactionsNuclear Reactions

• Alpha emissionAlpha emission

Note that mass number (A) goes down by 4 and atomic number (Z) goes down by 2.Nucleons (nuclear particles… protons and neutrons) are rearranged but conserved

Nuclear ReactionsNuclear Reactions

• Beta emissionBeta emission

Note that mass number (A) is unchanged and atomic number (Z) goes up by 1.

Other Types of Nuclear Other Types of Nuclear ReactionsReactions

Positron (Positron (00+1+1): a positive electron): a positive electron

Electron capture: Electron capture: the capture of an electron

207 207

Learning Check

What radioactive isotope is produced in the following bombardment of boron?

10B + 4He ? + 1n

5 2 0

Write Nuclear Equations!

Write the nuclear equation for the beta emitter Co-60.

Group Practice

• Work some problems together using ELMO

• See Nuclear Equations Worksheet – page 4 of Flinn ChemTopicTM Labs book (vol. 18)

Independent Practice Set

• Balancing Nuclear Equations – 1

• Balancing Nuclear Equations – 2 (Word Problems)

Part III

•Nuclear Stability

•Half-Life

Introduce Half-Life with Lab

• Half-Life of M&Ms (TAMU handout) or

• Half-Life of Licorice (TAMU Handout) or

• Half-Life with Pennies– IPC Lab Manual – pages 152 & 153

Nuclear Stability

• Depends on the neutron to proton ratio.

Band of Stability

Number of Neutrons, (N)

Number of Protons (Z)

What happens to an unstable nucleus?

• They will undergo decay

• The type of decay depends on the reason for the instability

What type of decay will happen if the nucleus contains too many neutrons?

• Beta Decay

Example:

C N + e

In N-14 the ratio of neutrons to protons is 1:1

14

7 -1

014

6

• Nuclei with atomic number > 83 (Bismuth) are radioactive

Radioactive Half-Life (t1/2 ):

• Through study of radioactive isotopes, scientists have defined the rate of instability as half-life

• In other words…. The time for half of the radioactive nuclei in a given sample to undergo decay

Common Radioactive Isotopes

Isotope Half-Life Radiation Emitted

Carbon-14 5,730 years

Radon-222 3.8 days

Uranium-235 7.0 x 108 years

Uranium-238 4.46 x 109 years

Radioactive Half-Life

• After one half life there is 1/2 of original sample left.

• After two half-lives, there will be

1/2 of the 1/2 = 1/4 the original sample.• After three half-lives, there will be 1/2 of the 1/4

(or 1/8) the original sample• ….And so on….

Graph of Amount of Remaining Nuclei vs Time

A=Aoe-t

A

Half-Life Related Calculations• How to calculate number of half-lives (1/2 x 1/2x…)• How to calculate how old something is (no. of half-

lives x time per half-life)• Calculate amount remaining (A) after a certain

number of half-lives

A = Ao (where Ao = original amount)

2n (where n = no. of half-lives)• Calculate percentage remaining

__1_x 100%

2n (where n = no. of half-lives)

Example

You have 100 g of radioactive C-14. The half-life of C-14 is 5,730 years.

• How many grams are left after one half-life? Answer: 100 g

50 g

• How many grams are left after two half-lives?

Problem

A sample of 3x107 Radon atoms are trapped

in a basement that is sealed. The half-life of

Radon is 3.83 days. How many radon atoms

are left after 31 days?

answer:1.2x105 atoms

Group and Independent Practice

• Determining Half-Lives Practice Set

– Practice 2 of problems as a group

Part IV

Fission and Fusion

From Bill Nye the Science Guy

• Nuclear Power – link to Discovery Education website

FISSION

Nuclear FissionNuclear Fission

Nuclear FissionNuclear FissionFission is the splitting of atomsFission is the splitting of atoms

These are usually very large, so that they are not as These are usually very large, so that they are not as

stablestable

Fission chain has three general steps:Fission chain has three general steps:

1.1. Initiation.Initiation. Reaction of a single atom starts the Reaction of a single atom starts the

chain (e.g., chain (e.g., 235235U + neutron)U + neutron)

2.2. PropagationPropagation. . 236236U fission releases neutrons that U fission releases neutrons that

initiate other fissionsinitiate other fissions

3. 3. Produces enormous amounts of energyProduces enormous amounts of energy

Nuclear Fission & Nuclear Fission & POWERPOWER

• Currently about 103 Currently about 103

nuclear power plants in nuclear power plants in

the U.S. and about 435 the U.S. and about 435

worldwide.worldwide.

• 17% of the world’s 17% of the world’s

energy comes from energy comes from

nuclear.nuclear.

Figure 19.6: Diagram of a nuclear power plant.

Fission

• Benefits– A lot of energy can be

produced from a small amount of raw material

• 1 ton of nuclear material = 1 million tons of coal or 1 million barrels of oil

– Clean source of energy generation – not air polluting like fossil fuels

– Long term source of fuel

• Concerns– Safety accidents have

potential for horrendous harm (immediate and long term, such as cancer)

– No good way to dispose of high level nuclear waste

– Expensive construction and maintenance costs

FUSION

Nuclear Fusion

Fusion

small nuclei combine

2H + 3H 4He + 1n +

1 1 2 0

Occurs in the sun and other stars

Energy

Nuclear Fusion

Fusion

• Excessive heat can not be contained

• Attempts at “cold” fusion have FAILED.

• “Hot” fusion is difficult to contain

Fusion

• Benefits– A lot of energy can be

produced from a small amount of raw material

• 1 ton of nuclear material = 1 million tons of coal or 1 million barrels of oil

– Clean source of energy generation – not air polluting like fossil fuels

– Long term source of fuel– Doesn’t create hazardous

radioactive wastes as does nuclear fission

• Concerns– Occur at extremely high

temperatures – like that of sun

– Cannot sustain the reactions long enough to be useful for power generation

– Safety accidents have potential for horrendous harm (immediate and long term, such as cancer)

– Expensive construction and maintenance costs

Part V

Uses of Nuclear Chemistry

Radiocarbon DatingRadiocarbon DatingRadioactive C-14 is formed in the upper atmosphere Radioactive C-14 is formed in the upper atmosphere

by nuclear reactions initiated by neutrons in by nuclear reactions initiated by neutrons in cosmic radiationcosmic radiation

1414N + N + 11oon ---> n ---> 1414C + C + 11HH

The C-14 is oxidized to COThe C-14 is oxidized to CO22, which circulates through , which circulates through

the biosphere.the biosphere.

When a plant dies, the C-14 is not replenished.When a plant dies, the C-14 is not replenished.

But the C-14 continues to decay with tBut the C-14 continues to decay with t1/21/2 = 5,730 years. = 5,730 years.

Activity of a sample can be used to date the sample.Activity of a sample can be used to date the sample.

Nuclear Medicine: Nuclear Medicine: ImagingImaging

Thyroid imaging using Tc-99mThyroid imaging using Tc-99m

Food Food IrradiationIrradiation

•Food can be irradiated with Food can be irradiated with rays from rays from 6060Co Co

or or 137137Cs.Cs.•Irradiated milk has a shelf life of 3 mo. Irradiated milk has a shelf life of 3 mo.

without refrigeration.without refrigeration.•USDA has approved irradiation of meats and USDA has approved irradiation of meats and

eggs.eggs.

Part VI

Hazards of Radiation

Effects of RadiationEffects of Radiation

Summary

• Nuclear Radiation can be naturally occurring or man-made

• Most of radiation we are exposed to is naturally occurring – alpha rays

• Alpha Radiation – weakest (blocked by paper or cloth)• Beta Radiation – medium (blocked by wood or foil)• Gamma Radiation – strongest (blocked by lead or

concrete)

• Key Nuclear Science Pioneers – Henri Beckerel, Marie

and Pierre Curie

Summary

• How to Write Nuclear Notation - see blue graphic organizer

• Symbols for:Beta Particles Alpha Particles

Positrons Neutrons

Gamma Rays γ

Atomic Mass

Atomic No. Element symbol

1n0

Summary• Balancing Nuclear Equations (Law of Conservation of

Mass)

• Add coefficients in front of nuclear particles

SUMMARY - Half-Life Calculations• How to calculate number of half-lives (1/2 x ½ x…) or

1/amount remaining (as decimal or fraction) = 2n where n = no. half-lives

remember percent remaining = 100 – percent decayed

• How to calculate how old something is (no. of half-lives x time per half-life)

• Calculate amount remaining (A) after a certain number of half-lives

A = Ao (where Ao = original amount)

2n (where n = no. of half-lives)• Calculate percentage remaining

__1_x 100%

2n (where n = no. of half-lives)

Summary– Describe the difference between:– fission (splitting atoms)

• 3 steps – Initiation– Propagation– Production of large amounts of energy

– fusion (combining nuclei)– Describe the pros and cons of each– Describe examples of fission and fusion

– Examples of beneficial and harmful radiation sources• Power generation• Medical imaging, diagnostics, disease treatments• Food safety• Other – historical dating, smoke detectors, etc.

– Know what percentage of US and world energy comes from nuclear material. Know the country that leads in nuclear usage.

Extra

• Discovery Learning Video – Chemistry Connections: Nuclear Changes

• Radioactivity Homework