Slide 1 Do Now What would be the product if radon-222 underwent decay to produce 1) an alpha...

Do NowWhat would be the product if radon-222 underwent decay to produce

1) an alpha particle polonium-218

2) a beta particle francium-222

3) a gamma particle radon-222

4) a positron emission astatine-222

Impact of Decay

type atomic notation DNp DNn DZ DA

alpha ‒2 ‒2 ‒2 ‒4

beta +1 ‒1 +1 0

gamma 0 0 0 0

positron ‒1 +1 ‒1 0

Do NowWhat would be the product if radon-222 underwent decay to produce

1) an alpha particle polonium-218

2) a beta particle francium-222

3) a gamma particle radon-222

4) a positron emission astatine-222

Nuclear Stability

SWBAT explain the factors that influence nuclear stability, the characteristics of the band of stability, and predict the radioactive decay path of a nuclei based on these principles

Write this in your notes

Why Are Some Nuclei Radioactive?• Some nuclei are radioactive• Some nuclei are stable• What factors determine this difference?

Factors in Nuclear Stability

1) (n/p) ratio

2) odd or even Np and Nn

3) atomic number


How does a nucleus stay together?

Note:1) A nucleus has multiple protons all very

close to each other2) Protons are positively charged3) Like charges repel each other

Why doesn't the nucleus blow apart?

Strong Nuclear Force

Strong Nuclear Force• A force that acts on subatomic particles

that are extremely close together• The strongest of the four fundamental

forces of the universe


Forces in the NucleusAttraction

The strong nuclear force attracts protons to protons, neutrons to

neutrons, and protons to neutrons

Repulsion

The electromagnetic force cause like charges to repel each other


The stability of the nucleus partially depends on the balance between attractive strong nuclear force and repulsive electromagnetic force.

1) Neutron to Proton Ratio• A key factor in the stability of a nuclei is the

neutron to proton ratio - the (n/p) ratio• Each proton contributes to both repulsion

and attraction in the nucleus• Each neutron contributes to attraction only

• At low mass numbers, a 1.0 (n/p) ratio seems optimum for stability

• As the mass number rises, the optimum (n/p) ratio rises to 1.5


Graph Np on x-axis

Graph Nn on y-axis

A black point represents every stable nuclei

All points lay between lines with slopes of 1.0 and 1.5

This collection of stable nuclei is known as the

BAND OF STABILITYWrite this in your notes

2) Odd and Even Np and Nn

• Having an even number of either protons or neutrons or both confers stability

• Stability believed to be derived from pairing of spin numbers

number of stable nuclei Np Nn %

148 even even 58%53 even odd

40%48 odd even5 odd odd 2%

Total: 254


The Stability Associated with Even Np & Nn

Creates Zig-Zag Shape

3) Atomic Number

All elements with atomic numbers greater than 83 are unstable and undergo spontaneous

radioactive decay


What does an unstable nuclei do?• If a nuclei is unstable, it will undergo

radioactive decay to make it more stable

• Each unstable nuclei will decay in a way that will address the source of instability

If Z is too high




If Z is too high Æ lower Z





If (n/p) is too high





If (n/p) is too high Æ lower (n/p)






If (n/p) is too low






If (n/p) is too low Æ raise (n/p)

Pathways to Nuclear Stability

type process Δp Δn impact when utilized




a decay à ‒2 ‒2 Z falls Z > 83





b decay n à p + e‒ +1 ‒1 n/p falls high n/p






positron emission p à n + e+ ‒1 +1 n/p rises low n/p

electron capture p + e‒ à n ‒1 +1 n/p rises low n/p


Electron Capture Write this in your notes

neutronproton electron

▬

• Electron capture is a nuclear process to improve nuclear stability

• A proton from the nucleus "captures" an electron from the electron cloud.

• Together they become a neutron which remains in the nucleus.

• Nuclear impact is same as positron emission• Opposite process from beta decay

• Not radioactive decay because no radiation is released

Day 2 Intro

Do Now

Po ª Pb ª Bi ª Tl

Some unstable isotopes need to undergo a series of radioactive decays to reach a stable isotope. These are called "decay chains". For example, polonium-213 suffers a-decay, then b-decay, and then another a decay to reach a stable isotope. Determine the products of each step of this decay chain.

Impact of Decay

type atomic notation DNp DNn DZ DA

alpha ‒2 ‒2 ‒2 ‒4

beta +1 ‒1 +1 0

gamma 0 0 0 0

positron ‒1 +1 ‒1 0

REVIEW

Forces in the NucleusAttraction

The strong nuclear force attracts protons to protons, neutrons to

neutrons, and protons to neutrons

Repulsion

The electromagnetic force cause like charges to repel each other

The stability of the nucleus partially depends on the balance between attractive strong nuclear force and repulsive electromagnetic force.

REVIEW

Factors in Nuclear Stability

1) (n/p) ratio

2) odd or even Np and Nn

3) atomic number

REVIEW

Graph Np on x-axis

Graph Nn on y-axis

A black point represents every stable nuclei

All points lay between lines with slopes of 1.0 and 1.5

This collection of stable nuclei is known as the

BAND OF STABILITY

REVIEW

2) Odd and Even Np and Nn

• Having an even number of either protons or neutrons or both confers stability

• Stability believed to be derived from pairing of spin numbers

number of stable nuclei Np Nn

148 even even53 even odd48 odd even5 odd odd

REVIEW

REVIEW






If (n/p) is too low Æ raise (n/p)

REVIEW







REVIEW

How Accurate Are These Predictions?

Graphic Analysis of Predictions• The band of stability is

the red line.

Too Many Neutrons• Any atom above the

red line will have a high n/p ratio

• These will be unstable and undergo a nuclear reaction to lower the n/p ratio

• Thus, any atom above the line should undergo beta decay

b decay

Too Many Protons• Any atom below the

red line will have a low n/p ratio

• These will be unstable and undergo a nuclear reaction to raise the n/p ratio

• Thus, any atom above the line should undergo positron emission or electron capture

b+ or e–

capture

Z is Too High• Any atom with Z > 83

will have a Z value that is too high

• These will be unstable and undergo a nuclear reaction to lower Z

• Thus, any atom with Z > 83 should undergo alpha decay.

adecay

Predicted Decay Trends on Graph

adecay

b+ or e–

capture

b decay

Predicted Observed

Predicted Decay Trends on Graph

adecay

b+ or e–

capture

b decay

Draw this in your notes

Check For Understanding 1

Predict the decay pathway of hydrogen-3

1) Z = Np = 1

2) A = 3, Nn = A - Np = 2

3) n/p = 2.0 (too high)

4) Need to lower n/p, so b-decay

5) helium-3Write this in your notes


Predict the decay pathway of plutonium-244

1) Z = Np = 94, Z > 83

2) Need to lower Z, so a-decay3) uranium-2404) or, n/p = 150/94 = 1.59 (too high)5) need to lower n/p, so b-decay6) americium-244



Predict the decay pathway of nitrogen-13

1) Z = Np = 7

2) A = 13, Nn = A - Np = 6

3) n/p = 0.86 (too low), need to raise n/p

4) positron emission or electron capture

5) carbon-13Write this in your notes

Independent Practice

Predict the radioactive decay pathway1) carbon-14

n/p = 1.3 (too high), reduce n, b-decay

2) radon-222 Z = 86 (Z>83), reduce p, a-decay

3) magnesium-22 n/p = 0.83 (too low), reduce p, positron emission

4) lead-214 n/p = 1.6 (too high), reduce n, b-decay


Predict the radioactive decay pathway1) carbon-14

n/p = 1.3 (too high), reduce n/p, b-decay

2) radon-222 Z = 86 (Z>83), reduce Z, a-decay, polonium-218 or n/p = 1.58 (too high), reduce n/p, b-decay, franconium-222

3) magnesium-22 n/p = 0.83 (too low), raise n/p, positron emission, sodium-22

4) lead-214 n/p = 1.6 (too high), reduce n/p, b-decay, bismuth-214

Day 3 Intro

Do Now• What are the primary forces acting on the

nucleus? How do they impact the particles in the nucleus and nuclear stability?

• What are the three factors used to estimate nuclear stability? What are the optimum values for these three factors?

Particle Review 1• Below are two nuclear processes.

A. How would each one change a nucleus? B. What is the name of each process? C. Under what circumstances would a nucleus want to

undergo each process?

–

+

–

+

proton

neutron

electron

positron

Particle Review 2

–

–

+

proton

neutron

electron

positron

• Below are two nuclear processes. A. How would each one change a nucleus? B. What is the name of each process? C. Under what circumstances would a nucleus want to


Analysis of Nuclear StabilityFluorine-16 is radioactive.1) Analyze all 3 factors of stability & determine which

need to be changed2) Predict decay pathway and product3) Reanalyzed the 3 factors of stability to determine if

they are now acceptable




too low LNp: oddNn: odd LZ < 83 J

F ª O + e





F ª O + eb+





JNp: evenNn: even J

Z < 83 J

F ª O + eb+

Analysis of Nuclear StabilityBoron-12 is radioactive.1) Analyze all 3 factors of stability & determine which



Analysis of Nuclear StabilityPolonium-209 is radioactive.1) Analyze all 3 factors of stability & determine which



Backup Slides

Check for Understanding

N ª C + e

Before AfterResults Analysis Result Analysis

n 6 7p 7 6

n/p ratio L Jodd/even p odd

n even K p evenn odd K

Z < 83 J < 83 J

Predict the decay pathway for nitrogen-13

Check for Understanding

H ª He + e


p 1 2n 2 1

n/p ratio L Lodd/even p odd

n even K p evenn odd K

Z < 83 J < 83 J

Predict the decay pathway for hydrogen-3

JKL


C ª N + e


n 8 7p 6 7

n/p ratio L Jodd/even p even

n even J p oddn odd L

Z < 83 J < 83 J

Predict the decay pathway for carbon-14


Rn ª Po + He


n 127 125p 86 84

n/p ratio J Jodd/even p even

n odd K p evenn odd L

Z > 83 L > 83 L

Predict the decay pathway for radon-222

Review of Objective

SWBAT explain the factors that influence nuclear stability, the characteristics of the band of stability, and predict the radioactive decay path of a nuclei based on these principles




b decay n à p + e‒ +1 ‒1 n/p falls high Nn

positron emission p à n + e+ ‒1 +1 n/p rises high Np

electron capture p + e‒ à n ‒1 +1 n/p rises high Np

Nuclei Decay to Become Stable

Outline 1• Why are some nuclei stable and others

radioactive?• Nuclear stability

– What are the natural forces & what is strong nuclear force– balance between strong nuclear attraction & electrostatic

repulsion– neutrons help stabilize because they contribute to strong

nuclear attraction without contributing electrostatic repulsion

Outline 2• Band of Stability

– Lighter nuclei are stable with a (n/p) ratio of 1:1– Heavier nuclei are stable with a (n/p) ratio of 1.5:1– Even numbers of protons & neutrons are more stable– No nuclei with >83 protons is stable wrt radioactive decay

• Nuclei outside the band of stability want in– >2000 nuclei known, only 279 are stable– Above the band, get rid of some neutrons– Below the band, get rid of some protons– >83 protons, get rid of protons and neutrons

Do Now• Below are two nuclear processes.

A. How would each one change a nucleus? B. What is the name of each process? C. Under what circumstances would a nucleus want to


‒+neutron

in the nucleusproton

in the nucleuselectronemitted

Nuclei Decay to Become Stable

Decay Trends on Graph

Note• The following examples have been chosen

because their radioactive decay pathways are easily predicted

• It is often difficult to predict if a nuclei will be radioactive, and if so, its pathway of decay

• Often the instability of the nuclei is caused by a concert of multiple factors

• Radioactivity and radioactive decay pathways are usually determined experimentally

Slide 1 Do Now What would be the product if radon-222 underwent decay to produce 1) an alpha...

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