notes: unit 14 nuclear chemistry - …...5/12/2016 2 radioactivity • is due to the proton-neutron...

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Regents Chemistry: Mr. Palermo

Notes: Unit 14 Nuclear Chemistry

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www.mrpalermo.com

KEY IDEAS:

Stability of isotopes is based in the ratio of neutrons and protons in its nucleus. Although most nuclei are stable, some are unstable and spontaneously decay, emitting radiation. (3.1o)

Each radioactive isotope has a specific mode and rate of decay (half-life). (4.4a) A change in the nucleus of an atom that converts it from one element to another is called transmutation.

This can occur naturally or can be induced by the bombardment of the nucleus by high-energy particles. (5.3a)

Spontaneous decay can involve the release of alpha particles, beta particles, positrons, and/or gamma radiation from the nucleus of an unstable isotope. These emissions differ in mass, charge, ionizing power, and penetrating power. (3.1p)

Nuclear reactions include natural and artificial transmutation, fission, and fusion. (4.4b) There are benefits and risks associated with fission and fusion reactions. (4.4f) Nuclear reactions can be represented by equations that include symbols which represent atomic nuclei

(with the mass number and atomic number), subatomic particles (with mass number and charge), and/or emissions such as gamma radiation. (4.4c).

Energy released in a nuclear reaction (fission or fusion) comes from the fractional amount of mass converted into energy. Nuclear changes convert matter into energy. (5.3b)

Energy released during nuclear reactions is much greater than the energy released during chemical reactions. (5.3c)

There are inherent risks associated with radioactivity and the use of radioactive isotopes. Risks can include biological exposure, long-term storage and disposal, and nuclear accidents. (4.4e)

Radioactive isotopes have many beneficial uses. Radioactive isotopes are used in medicine and industrial chemistry, e.g., radioactive dating, tracing chemical and biological processes, industrial measurement, nuclear power, and detection and treatment of disease. (4.4d)

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UNIT 14: NUCLEAR CHEMISTRY

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LESSON 14.1 NUCLEAR CHEMISTRY

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Objective: By the end of this video you should be able to:

Identify the type of nuclear decay mode

Construct nuclear equations for alpha,

beta and positron decay

Determine the penetrating power of each emission

Atomic Notation:

Subtract atomic number from mass

number to find the NEUTRONS

ISOTOPES: Same element different

number of neutrons

• In the simplest terms, an unstable (radioactive) nucleus of an atom

breaks apart into smaller parts.

• Transmutation: Occurs when the

unstable element (radioactive)

decays into new element.

• ALWAYS TURNS INTO A MORE STABLE ELEMENT

Radioactive Decay Stability of Nuclei

• Large Atoms

- Elements with an atomic number greater

than 83 are naturally unstable

(radioactive.)

• Small atoms

- When an atom’s mass is not its typical

mass on the periodic table

- C-13 & C-14

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RADIOACTIVITY

• Is due to the proton-neutron ratio. The band

of stability refers to atoms that are stable due

to stable proton-neutron ratios.

Table O- Types of Decay (Radiation)

Number on the upper left is the mass Number on the lower left is the charge

• When nuclei of unstable atoms emit radiation (Table O) naturally & form a

new substance

• REMEMBER….DON’T BREAK THE LAW

- The Laws of Conservation of Mass &

Charge

- in a nuclear reaction, Mass & Charge

must be conserved

Natural Transmutation

Table N: Decay Modes for Selected Nuclides

RADIOACTIVITY- BETA DECAY

• Atoms above the belt

have too many

neutrons and will beta

decay due to this.

• The beta particle is an

electron created when

a neutron decays.

I 131

53 Xe 131

54 + e 0

−1

0

−1 e 0

−1 or

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Example: Beta decay: 234Th undergoes beta decay

234Th 0e + 234Pa

• The total mass on the left must equal the

total mass on the right (234 = 0 + 234)

• The total charge on the left must equal the

total charge on the right (90 = -1 + 91)

90 -1 91

Example

Construct the nuclear decay equation for Carbon-14 (remember that

mass and charge must be conserved)

Check your understanding

Can you identify the type of nuclear decay mode

Can you construct nuclear equations

for beta and decay

RADIOACTIVITY- POSITRON EMISSION

• Atoms below this belt

have too many

protons and positron

decay.

• The positron is the

opposite of a beta

particle.

C 11

6 B 11

5 + e 0

1

0

+1 e 0

+1 or

Example: Positron emission: 37K undergoes positron decay

37K 0e + 37Ar

• The total of the mass numbers on the left must equal the total on the right (37 = 0 + 37)

• The total charge on the left must equal the total charge on the right (19 = 1 + 18)

19 +1 18

Example:

Construct the nuclear decay equation for Calcium-37 (remember that

mass and charge must be conserved)

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Check your understanding:



for positron decay

Radioactivity- Alpha decay

• Atoms with 82 or more protons alpha decay (too many protons and

neutrons)

• Alpha particles are weak due to their

mass.

• Alpha particles are the helium nuclei.

U 238

92 Th 234

90 He 4

2 +

He 4

2 α 4

2 or

Example: Alpha decay: 238U undergoes

alpha decay

238U 4He + 234Th

• The total mass on the left must equal the

total mass on the right (238 = 4 + 234)

• The total charge on the left must equal the

total charge on the right (92 = 2 + 90)

92 2 90

Example:

• Complete the example problems below showing

ALPHA DECAY (remember, CHARGE and MASS must be conserved!)




for alpha decay

Radioactivity- Gamma decay

• Strongest particle.

• Accompanies most decay.

• Usually not written due to the fact

that it cannot change the mass or

charge of any of the species.

0

0

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Penetrating Power

Most penetrating

power

Least penetrating

power

Radiation is charged: Can be separated by a magnetic field


Can you determine the penetrating power of each emission

You must be able to:

Differentiate between artificial and

natural transmutation

Identify the type of nuclear decay mode

Construct nuclear equations for alpha,

beta and positron decay

Determine the penetrating power of

each emission

LESSON 14.2 HALF LIVES

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Objective: By the end of this lesson you should be able to:

Calculate given two of the three variables the:

amount remaining

the fraction remaining

the half life

number of half lives

the original mass of a radioactive isotope

Time elapsed

HALF-LIFE

• Half Life: is the time it takes for ½ of the

atoms of a radioisotope to decay.

Calculating Half Life

• After one half life 50% or ½ the radioactive element is still present.

• After two half lives 25% or 1/4 the radioactive element is still present.

• After three half lives 12.5% or 1/8 the radioactive element is still present.

• This continues forever, the number will never be zero.

• The half lives are listed on Table N.

Table N- Half life Time

• The SHORTER THE HALF LIFE of an isotope the LESS STABLE it is.

• The LONGER THE HALF LIFE of an

isotope the MORE STABLE it is.

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HALF LIFE PROBLEMS

• If a sample of I-131 has an original mass of

52.0g what mass will remain after 40 days?

Example: Amount Remaining

If a sample of I-131 has an original mass of 64.0g what

mass will remain after 32 days?

1. Determine the number of half lives that have taken

place using table N

2. Cut original mass in

half by the # of half lives

Example: Amount Remaining

Total

Time elapsed

= 32

8 = 4 Cut in half

4 times Half life time

from Table N

(# of Half Lives)

(Mass)

64 32 16 8 4

4g of I-131

remain

Practice

If a sample of Cs-137 has an original mass of 52.0g what mass will remain after 150 years?

26.0 13.0 6.50 3.25 1.63 1 2 3 4 5

52.0

After 150 years, 1.63g of

Cs-137 remain

Total

Time elapsed

= 150

30 = 5 Cut in half


from Table N

0

Example: Fraction Remaining

If a sample of Cs-137 has an original mass of 52.0g what fraction will remain after 150 years?

Same set up but you Half the fractions instead of the mass

1/2 1/4 1/8 1/16 1/32 1 2 3 4 5

1 0

Total

Time elapsed

= 150

30 = 5 Cut in half


from Table N

After 150 years, 1/32 of

Cs-137 remain

Practice

If a sample of Fe-53 has an original mass of 52.0g what fraction will remain after 25.5 minutes?

Same set up but you

Half the fractions

1/2 1/4 1/8 1 2 3

1 0

Total

Time elapsed

= 25.5

8.51 = 3 Cut in half


from Table N

After 25.5 minutes, 1/8 of

Fe-53 remains

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Can you calculate given two of the three

variables the:

- amount remaining

- the fraction remaining

Example: Number of half-lives

How many half-life periods will it take for 50 grams of

Tc-99 to decay to 6.25g?

Find the number of half lives by halving the original mass until you get to the final mass

25.0 12.5 6.25 1 2 3

50.0 0

It takes 3 half-life periods

for TC-99 to decay to 6.25 grams

Practice:

How many half-life periods will it take for 100 grams of

I-131 to decay to 25g?

Find the number of half lives by halving the original mass until you get to the final mass

50 25 1 2

100 0

It takes 2 half-life periods

for I-131 to decay to 25g

Example: half-life

What is the half-life of a 500 gram sample of a radioactive element if 125 grams remains after 20 hours?

1. Find the number of half lives by halving the original mass until you get to the final mass

2. Divide the total time elapsed by the number of half life periods you calculated in step 1.

250 125 1 2

500 0

= 2 half life periods

Total

Time elapsed

= 20

x = 2 Half life

periods Half life time

from Table N

20/2 = 10 hours

Practice

What is the half-life of a 500 gram sample of a radioactive element if 125 grams remains after 20 hours?

1. Find the number of half lives by halving the original mass until you get to the final mass

2. Divide the total time elapsed by the number of half life periods you calculated in step 1.

250 125 1 2

500 0

= 2 half life periods

Total

Time elapsed

= 20

x = 2 Half life


from Table N

20/2 = 10 hours



variables the:

- the half life

- number of half lives

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Example: Original Mass

The half life of Tc-99 (used in brain tumors) is 6 hours. If 10 micrograms are left after 24 hrs, how much was administered to the patient originally?

1. Divide the times to obtain your amount of half life

periods

2. Work backwards and double the mass 4 times

The original mass was 160 micrograms

Total

Time elapsed

= 24

6 = 4 Half life


from Table N

80 40 20 10 4 3 2 1

160 0

Practice:

After 37 hours, 2g remains unchanged from a sample of K-42. How much was in the original sample?

Total

Time elapsed

= 37

12.36 = 3 Half life


from Table N

8 4 2 1 3 2 1 0

The original mass was 8g micrograms

MORE EXAMPLES:

Example: Time Elapsed

How long will it take for a 400 grams sample of P-32 to decay to 50 grams?

1. Find the half lives by dividing the original mass in half until it hits your final mass. 400/2 = 200/2 = 100/2 = 50 3HL

2. Look up the half live on table N and multiple that time by the number of half lives you calculated. 14.3 days * 3 = 42.9 days



variables the:

- the original mass of a radioactive isotope

- Time elapsed

REMEMBER YOU ONLY HALF MASS

YOU NEVER HALF TIME!!!!!!

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You must be able to:

Calculate given two of the three variables the:

- amount remaining

- the fraction remaining

- the half life

- number of half lives

- the original mass of a radioactive isotope

- Time elapsed

LESSON 14.3 NUCLEAR FISSION VS FUSION

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Differentiate between natural and artificial transmutation

Distinguish between fusion and fission reactions

Compare the advantages and disadvantages of fusion and fission reactions

Artificial Transmutation

• A transmutation that occurs from bombarding a nucleus w/ high

energy particles

ARTIFICIAL VS NATURAL TRANSMUTATION

Artificial

• Always 2 reactants

• Not spontaneous

Natural

• Always 1 reactant

• Spontaneous


• Can you differentiate between natural and artificial transmutation

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Nuclear Reactions

• If you add the actual masses of all the protons,

neutrons and electrons in an atom and compare it to the atom’s actual mass, mass is lost. This is known

as mass deficit. Mass is converted to energy! E=mc2

• The energy holds the subatomic particles together and is called the binding energy.

• When these reactions occur, small amounts of mass can be created into LARGE amounts of energy.

• This energy can be harvested in fission and fusion reactors for everyday energy use.

FISSION REACTIONS

• A neutron is shot at a radioactive

source which splits producing energy.

1n + 235U --> 236U --> 142Ba + 91Kr + 3 1n + energy 0 92 92 56 36 0

If the number of neutrons released is not controlled a chain reaction will occur.

This is the type of reaction used in

nuclear bombs.

NOTE: ENERGY is also produced in the above nuclear reaction…

Chain Reaction

• A series of reactions where each reaction is initiated by the energy

produced in the previous reaction

Fission Reactors

The reaction’s energy is converted to steam

which turns and turbine system, creating electrical energy from nuclear energy.

Fission Reactors

• Fuel rods contain the

fissionable radioactive

source (critical mass)

• Control rods can regulate

the neutrons absorbed

(controlling the chain

reaction.)

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Nuclear power

• In America, about 20% electricity

generated by nuclear fission

• Imagine:

- Nuclear-powered car

- Fuel = pencil-sized U-cylinder

- Energy = 1000 20-gallon tanks of gasoline

- Refuel every 1000 weeks (about 20 years)

FUSION REACTIONS

• Involves the combining (fusing) of nuclei to produce heavier ones.

• Ex. 2H + 3H 4He + 1n

Hydrogen atoms combine to form helium in a star.

How do they know the Sun is made up of Helium?

• Observe helium’s bright line spectrum

from the sun


• Can you distinguish between fusion and fission reactions

FUSION REACTIONS

ADVANTAGES DISADVANTAGES

• Produces more energy

• Materials more readily

available

• Less waste

• Less danger (no chain

reaction)

• Too Expensive


Can you compare the advantages and disadvantages of fusion and

fission reactions

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You should be able to:

Differentiate between natural and artificial transmutation

Distinguish between fusion and fission

reactions

Compare the advantages and disadvantages of fusion and fission

reactions

LESSON 14.4 BENEFITS & RISKS OF NUCLEAR POWER

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Identify specific uses of some common radioisotopes

Identify the risks/benefits of

radioactivity USES OF RADIOACTIVE ISOTOPES

DATING MATERIALS

• Carbon-14 used to date organic

remains

• Uranium used to date rocks

Am-241 is used in Smoke detectors

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MEDICAL APPLICATIONS

• Must have short half-life and quickly eliminated from body

• I-131 thyroid (treat hyperthyroidism)

• Co-60 used to treat cancer

Medical Applications:

• Tc-99 used to detect tumors


• Can you identify specific uses of some common radioisotopes

DANGERS/RISKS OF RADIOACTIVITY

• Damage to tissue

• Gene mutation

• Pollution due to radioactive wastes

• Accidents from nuclear reactors

FISSION

• The fission reaction produces radioactive waste that must be stored.

• Currently the waste is placed in large lead boxes under ground around the country.

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YUCCA MOUNTAIN

• The Yucca Mountain, in

Nevada, is a large long

term storage facility for

nuclear waste and testing.


• Can you identify the risks/benefits of radioactivity

You should be able to:

• Identify specific uses of some common radioisotopes

• Identify the risks/benefits of

radioactivity

notes: unit 14 nuclear chemistry - …...5/12/2016 2 radioactivity • is due to the proton-neutron...

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