1. Half-Life of Radioactive Elements
November 15, 2017
Half-Life of Radioactive Elements
Nuclear Chemistry
Learning Target: I CAN define half life and apply half life skills to determine the amount of radioactive element left after a number of half life cycles

2. November 15, 2017
Do Now (4 min)
Learning target: I CAN define half life and apply half life skills to determine the amount of radioactive element left after a number of half life cycles
Answer on your Do Now Sheet:
Using Table N, what is the value of the half-life for Iodine-131?
How long would it take for half a sample of Iodine-131 to decay?
Learning Target: I CAN define half life and apply half life skills to determine the amount of radioactive element left after a number of half life cycles

3. announcements November 15, 2017 Lab 6 – due Friday, November 17
Homework – Half life worksheet – due Friday, November 17
Test (nuclear chemistry) – Monday, November 20
Test corrections (periodic trends) – Due next Monday
Must follow test protocol (on weebly)
Afterschool tutoring: Wednesdays 3 – 4 PM
Learning Target: I CAN define half life and apply half life skills to determine the amount of radioactive element left after a number of half life cycles

4. November 15, 2017
Half life: t1/2
Half life: The time required for one half of the nuclei in a given sample to decay.
After each half life the mass of sample remaining is half.
Different isotopes have different half lives. Use table N
Learning Target: I CAN define half life and apply half life skills to determine the amount of radioactive element left after a number of half life cycles

5. Common Radioactive Isotopes
November 15, 2017
Common Radioactive Isotopes
Isotope Half-Life Radiation Emitted
Carbon ,730 years b, g
Radon days a
Uranium x 108 years a, g
Uranium x 109 years a
Learning Target: I CAN define half life and apply half life skills to determine the amount of radioactive element left after a number of half life cycles

6. Common Radioactive Isotopes
November 15, 2017
Common Radioactive Isotopes
Learning Target: I CAN define half life and apply half life skills to determine the amount of radioactive element left after a number of half life cycles

7. November 15, 2017
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.
Learning Target: I CAN define half life and apply half life skills to determine the amount of radioactive element left after a number of half life cycles

8. Try it yourself! (1 min)
What fraction of a radioactive sample would be left after 4 half-lifes?
Original amount  first half life  second half life  third half life  fourth half life
 ½  ¼  /  /16
There is 1/16 of the original sample left after 4 half lifes
Learning Target: I CAN define half life and apply half life skills to determine the amount of radioactive element left after a number of half life cycles
November 15, 2017

9. Graph of Amount of Remaining Nuclei vs Time
November 15, 2017
Graph of Amount of Remaining Nuclei vs Time A
Learning Target: I CAN define half life and apply half life skills to determine the amount of radioactive element left after a number of half life cycles

10. Half life: Example problem
November 15, 2017
Half life: Example problem
You have 100 g of radioactive C-14. The half-life of C-14 is 5730 years.
How many grams are left after one half-life? Answer:50 g
How many grams are left after two half-lives?
Learning Target: I CAN define half life and apply half life skills to determine the amount of radioactive element left after a number of half life cycles

11. Half life: Example problem
November 15, 2017
Half life: Example problem
If 80 g of a radioactive sample decays to 10 g in 30 min what is the element’s half life? HINT: what is the initial amount? What is half of that? And half of that?
Learning Target: I CAN define half life and apply half life skills to determine the amount of radioactive element left after a number of half life cycles

12. Using table N example problem
November 15, 2017
Using table N example problem
How many days will take a sample of I-131 to undergo three half life periods?
Learning Target: I CAN define half life and apply half life skills to determine the amount of radioactive element left after a number of half life cycles

13. Final mass example problem
November 15, 2017
Final mass example problem
What is the total mass of Rn-222 remaining in an original mass 160 mg sample of Rn-222 after 19.1 days?
Learning Target: I CAN define half life and apply half life skills to determine the amount of radioactive element left after a number of half life cycles

14. Regents questions (15 min)
November 15, 2017
Regents questions (15 min)
groups of 3
Practice regents-level questions of half-life
Must finish at least 15 in class
Turn in individual work
Remainder due Friday, November 17
Learning Target: I CAN define half life and apply half life skills to determine the amount of radioactive element left after a number of half life cycles

15. Remainder for homework
November 15, 2017
Remainder for homework
Complete the remainder of the worksheet for homework – due Friday, November 17
Learning Target: I CAN define half life and apply half life skills to determine the amount of radioactive element left after a number of half life cycles

16. Exit ticket (3 min) November 15, 2017 On a separate sheet of paper:
How long would it take for a 100 g sample of Iodine-131 to decay to 12.5g?
Learning Target: I CAN define half life and apply half life skills to determine the amount of radioactive element left after a number of half life cycles