Chemistry Day 15 Monday, October 1 st Tuesday, October 2 nd, 2018
Do-Now: VN: Nuclear Review 1. Write down today s FLT 2. What does the atomic number represent? 3. What does alpha decay do to the atomic number of an element? 4. What does beta decay do to the atomic number of an element? 5. How are protons able to be so close together in the nucleus of an atom? Finished? Have a calculator handy for today. We will take our notes on this same paper.
Planner: Lab corrections (separate paper) Ch. 19 Quiz bring calculators Study notes, old quizzes, textbook Table of Contents #2: 6. VN: Nuclear Review 7. Ch. 19 CN C 8. Half-Life WS
Video Notes We will watch a video clip that should REVIEW a lot of the nuclear chemistry topics we ve discussed (It reviews them very quickly) While watching, write down five facts or examples that are new to you J
FLT I will be able to perform calculations involving half-life by completing Ch. 19 CN Part C Standard HS-PS1-8: Develop models to illustrate the changes in the composition of the nucleus of the atom and the energy released during the processes of fission, fusion, and radioactive decay
Notes Protocol Title your notes & add assignment # Complete Cornell-style Copy down all bolded ideas Noise level 0 Raise hand to question/comment Be prepared to pair-share-respond
Ch. 19 CN C: Half-Life
Recall What are isotopes? Why do some isotopes decay?
Half-Life It can be difficult to determine the ages of objects by sight alone. Radioactivity provides a method to determine age by measuring relative amounts of remaining radioactive material to stable products formed.
Half-Life Half-Life (t 1/2 ) = time required for ½ of a radioactive nuclei sample to decay After each half-life, half of the existing radioactive atoms have decayed into atoms of a new element
Half-Life After one half-life, ½ of the sample remains After two half-lives, ½ x ½ of the sample remains ( ¼ ) After three half-lives, ½ x ½ x ½ of the sample remains ( 1/8 )
Working with Half-Life
Half-Life Example: Thorium-234 has a half life of 24.1 days After 24.1 days ½ of the thorium remains 2 half lives = 48.2 days After 48.2 days ¼ of the thorium remains 3 half lives = 72.3 days After 72.3 days 1/8 of the thorium remains
Half-Life Half-lives can be as short as a fraction of a second, and as long as billions of years For example, Uranium-238 has a half life of 4.46 x 10 9 years Half-lives can be used to estimate the ages of objects based on the rate of decay
Tidbits on Decay
Carbon Dating Carbon dating = estimates ages using the ratio of carbon-12 vs. carbon-14. Stable carbon-12 and radioactive carbon-14 exist naturally in a constant ratio. When an organism dies, carbon-14 stops being created and slowly decays. Carbon dating only works for organisms less than 50 000 years old.
The Rate of Radioactive Decay Decay curves = show the rate of decay (number of isotopes vs. half-life) The curve shows the relationship between half-life and % of original substance remaining.
Solving Problems
Half-Life Half-life measures the rate of radioactive decay. Strontium-90 has a half-life of 29 years. If you have 10 g of strontium-90 today. there will be 5.0 g remaining in 29 years.
Half-Life Example: Carbon-14 decays with a t 1/2 of 5730 years. You start with a mass of 2.00 g of carbon-14 1. How long is three half-lives? 2. How many grams of the isotope remain at the end of three half-lives?
Solve on your notes: Try one! A sample of thorium-234 has a half-life of 24.1 days. 1. How many half-lives are in 48.2 days? 2. How much thorium will be left after 48.2 days (answer as a fraction)?
Solve on your notes: Try one! Manganese-56 is a beta emitter with a halflife of 2.6 hours. 1. How many half-lives are in 10.4 hours? 2. What is the mass of a 1.0-mg sample of manganese-56 at the end of 10.4 hours?
Half-Life Problems: Fractions
Recall Half-lives can be modeled graphically using an exponential decay function
Half-Life We can calculate the relative amount left using an exponential decay equation:
Half-Life Or, in other words: The fraction remaining of an isotope (often expressed as a decimal) would be:
Half-Life Example: Fluorine-21 has a half-life of 4 seconds. What fraction of the original nuclei would remain after 1 minute?
Half-Life Try this one: The half-life of Th-227 is 18.2 days. What fraction of a sample remains after 1 day? Solution: First find t/h = 1 day/18.2 days = 0.055 Second (1/2) n = (1/2) 0.055 =0.963 of the original amount remains
Summary A half-life is the length of time required for half the nuclei in a sample of a radioactive isotope to decay into its products.
Pair-Share-Respond 1. What is a half-life? 2. The half-life of hydrogen-3 is 12.26 years. How long are two half-lives? 3. If you have 0.456mg of hydrogen-3, how much remains after two half-lives?
CW Complete the WS questions (half-life) Complete on separate paper Show ALL formulas, work and units Work with a partner. Check each problem.
Chemistry Day 16 Wednesday, October 3 rd Thursday, October 4 th, 2018
Do-Now: Ch. 19 Quiz Review Do-Now 1. Write down today s FLT 2. What does the mass number represent? 3. What is meant by the term transmutation? 4. Polonium-218 has a half-life of 3.0 minutes. How many half-lives are in 15 minutes? Show ALL work and units!! 5. How many half-lives are required to reduce 1 a sample by? 32 Finished? Take out your planner, ToC, calculator, and reference sheet
Planner: Clear your missing work Get review packet stamped (read last page) Study and practice problems for unit test Table of Contents #2: 9. Ch. 19 Quiz Review Do-Now 10. Unit 1 Review Packet
Quiz/Test Protocol Noise level 0 Eyes on own paper Mark answers clearly Do your best J Flip over when done
FLT I will be able to review for my unit test by completing the Unit Review Packet Standard HS-PS1-8: Develop models to illustrate the changes in the composition of the nucleus of the atom and the energy released during the processes of fission, fusion, and radioactive decay
Chemistry Day 17 Friday, October 5 th Monday, October 8 th, 2018
Do-Now: Unit 1 Test Day Do-Now 1. Write down today s FLT 2. Write down one question you have about the test (topic-wise or format-wise). 3. The change from a solid to a is called. 4. When doing calculations, I need to always include. 5. Correct Dalton by completing the sentence frame: While I agree that atoms of the same element, I disagree that because atoms of the same element can. 6. What should you always remember when solving half-life problems? 7. Take five minutes to review for the test. Take out your planner and ToC
Announcements Unit Test today J College Testing Day Wednesday 10/10 Ø Testing 7:45-11:30 (9 th, 12 th graders have assembly 10:15-11:32) Ø P. 4: 11:38-12:28 Ø P. 5: 12:34-1:24 Ø Lunch: 1:24-1:54 Ø P. 6: 2:00-2:45
Planner: Clear missing work & stamps Read Ch. 11 the material is a little bit challenging! Bring textbooks next class Table of Contents #2: 11. Unit 1 Test Day Do-Now 12. Basic Atomic Structure WS
FLT I will be able to demonstrate my mastery of atomic chemistry by completing the Unit 1 Test Standard HS-PS1-8: Develop models to illustrate the changes in the composition of the nucleus of the atom and the energy released during the processes of fission, fusion, and radioactive decay