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Objective: I can write a nuclear reaction equation and calculate the age of a sample using radioactive decay data.

- Agenda:
- Catalyst
- Mouse trap reactor
- Radioactive decay and nuclear reactions practice
- Portfolio Build

- In the penny lab, each trial represented one half-life. About what fraction of the pennies were removed each trial? (In other words, what does “half-life” mean?)

- Materials: Nuclear Chemistry handouts and homework

Video: movies file – mouse trap reactor regular and slow motion

Model: Mouse Trap ReactorVideo Focus Questions:

- In what ways does the mouse trap reactor model simulate a nuclear chain reaction?
- How is an actual nuclear chain reaction different from the mouse trap model?

Materials

- Nuclear chemistry handouts
- Nuclear energy article
- Unit 11: Nuclear Chemistry – Writing Nuclear Equations
- Nuclear chemistry work sheet
- Homework assignments:
- Due Next Class: Read pp. 658-666 Problems p. 666 #1, 2, 3, 5, 6, 7, 8
- Due Next Class: Read pp. 648-657 Problems p. 670 #34, 35 p. 671 #52, 54, 58, 60, 61, 62
- Last week: Read p. 642-643, 648-657 practice p. 653 #1-4; problems p. 657 #1, 2, 5, 6
- Last week: Read p. 658-666 Do problems: p. 666 #4, 9, 10, p. 669 #25, 26, 27

Quick Check:

- A beta particle is a(n)
- proton
- Neutron
- Electron
- Helium nucleus

Quick Check:

- A gamma ray can penetrate
- Skin
- A sheet of paper
- A 2-cm thick piece of aluminum
- All of the above

Sample Problem: Nuclear equations

p. 670 #32: When a radon-222 nuclear decays, an alpha particle is emitted. Write the nuclear equation to show what happens when a radon-222 nucleus decays.

222

Rn 86

4

He + 2

218

Po

84

Sample Problem: Nuclear equations

p. 671 #47: The radiation given off by iodine-131 in the form of beta particles is used to treat cancer of the thyroid gland. Write the nuclear equation to describe the decay of an iodine-131 nucleus.

131

I 53

0

e +

-1

131

Xe

54

Sample Problem: Radioactive dating

p. 660 #1: Assuming a half-life of 1599 y, how many years will be needed for the decay of 15/16 of a given sample.

- What is the question asking?
- # years for 15/16 of a sample to undergo radioactive decay
- How many half-lives must pass to decay 15/16 of a sample?
- Use the half-life pattern:
- 1 → ½ → ¼ → 1/8 → 1/16 → 1/32 → 1/64
- This pattern shows how much of an original sample is left after each half-life.
- For 15/16 to decay, 4 half-lives pass
- 1599 y x 4 = 6396 y

Sample: Radioactive dating

p. 662 #1: The half-life of polonium-210 is 138.4 days. How many mg of polonium-210 remain after 415.2 days if you start with 2.0 mg of the isotope?

- What is the question asking?
- How much Po is left after 415.2 days
- How many half-lives passed in 415.2 days?
- Divide: time/half-life
- 415.2 d/ 138.4 d = 3 half-lives
- Use the half-life pattern to determine the fraction of the sample left over: 1 → ½ → ¼ → 1/8
- Multiply the fraction by the original mass:
- 1/8 x 2.0 mg = ¼ mg or 0.25 mg

Practice

- Complete All Nuclear chemistry handouts
- Nuclear energy article
- Unit 11: Nuclear Chemistry – Writing Nuclear Equations
- Nuclear chemistry work sheet
- Homework assignments:
- Due Next Class: Read pp. 658-666 Problems p. 666 #1, 2, 3, 5, 6, 7, 8
- Due Next Class: Read pp. 648-657 Problems p. 670 #34, 35 p. 671 #52, 54, 58, 60, 61, 62
- Last week: Read p. 642-643, 648-657 practice p. 653 #1-4; problems p. 657 #1, 2, 5, 6
- Last week: Read p. 658-666 Do problems: p. 666 #4, 9, 10, p. 669 #25, 26, 27

Announcements

- Grades:
- You may pick up your benchmark grade report at student led conferences.
- Make up work:
- Make up assignments are posted on the board.
- Tutoring:
- Tutoring is Friday at 3:45.
- Worksheets and study guides:
- Do not throw away any Semester 2 materials. You need these to study for the CST.

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