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December 6, 2016

December 6, 2016. What do you know about nuclear energy or reactions? List at least one thing! Announcements: University of Texas due date is extended to Tuesday, Dec 13 th at 11:59 p.m. Test will be Tuesday. Busy weeks ahead- Keep your head in the game!!. Goals.

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December 6, 2016

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  1. December 6, 2016 What do you know about nuclear energy or reactions? List at least one thing! Announcements: University of Texas due date is extended to Tuesday, Dec 13th at 11:59 p.m. Test will be Tuesday. Busy weeks ahead- Keep your head in the game!!

  2. Goals • To explain the difference between fusion and fission • To describe half life and solve problems using half life

  3. Nuclear Chemistry • An element can have both stable and unstable isotopes Ex: • C-12 is stable so there is no nuclear decay (equal #s of p+ and n0) • C-14 is unstable and radioactive

  4. Nuclear Chemistry • A special force called the strong nuclear force holds the p and the n in the nucleus together. This force occurs over a very short distance.

  5. Nuclear Chemistry • Because of the strong nuclear force, the n and p attract other n and p. • *n have no charge and they do not repel each other or the protons. • *p repel each other with the electric force and attract each other with the strong nuclear force.

  6. Nuclear Chemistry • In stable nuclei, the attractive forces (strong nuclear) are stronger than the repulsive forces (electric).

  7. Nuclear Fission • Fission- The process by which a nucleus splits into two or more smaller fragments, releasing neutrons and energy. • The production of lighter nuclei from heavy nuclei • Used in nuclear power plants

  8. Nuclear Fission • When U-235 is bombarded by neutrons, the products of the reaction include 2 lighter nuclei that include Ba and Kr together with neutrons and energy • Each dividing nucleus releases about 3.2 x 10-11 joules of energy.

  9. Nuclear Fission • Some of the mass of the particles before the fission reaction is turned into energy after the reaction.

  10. Nuclear Fission • matter  energy • mass-energy equation • E=mc2 Einstein • A small loss of mass results in a great amount of energy that is given off.

  11. Nuclear Fusion • Fusion – The process in which light nuclei combine at extremely high temperatures, forming heavier nuclei and releasing energy. • Energy is also obtained during the fusion process

  12. Nuclear Fusion • Stars and Sun: Energy is produced when H nuclei combine • We need a large amount of energy to start a fusion reaction so that the H nuclei can be brought together and overcome the electric forces • This energy is provided by the high temperature • Often called thermonuclear fusion

  13. Homework • Part 1 • Read the article and answer the questions • Part 2 • Number 3: How is fusion different from fission? • Number 5: Change Fission to Fusion in the second part of the question • Number 8: Challenge question, use the box of chemical reactions (bottom right) on the information page to help you out

  14. December 7, 2016 How is nuclear fusion different from nuclear fission? What causes elements to be “radioactive”?

  15. Goals • To describe half life and solve problems using half life

  16. Radioactive Decay Rates • Half life- The time required for half of the sample of radioactive nuclei to decay.

  17. Radioactive Decay Rates • 1st half life  ½ sample remains unchanged • 2nd half life-> ¼ sample remains unchanged • 3rd half life -> 1/8 sample remains • 4th half life - > 1/16 sample remains • Eventually the entire sample will decay

  18. Radioactive Decay Rates 2. With each successive half life, half of the remaining sample decays to form another element. • Different radioactive isotopes have different half lives. • Half lives can last from nanoseconds billions of years

  19. Radioactive Decay Rates 3. If we know how much of the isotope is present at the beginning, we can predict how old the object is. • Rocks 40K decays to 40Ar. • The ratio of 40K to 40Ar is smaller in older rocks ( We have more 40Ar than 40K)

  20. Radioactive Decay Rates c. We can look at the ratios between C-12 and C-14 to determine the age of animal remains or plant remains.

  21. EXAMPLE: Thallium-208 has a half-life of 3.053 min. How long will it take for 120.0 g to decay to 7.50 g? • To do half life problems, make a chart with 4 columns 0 (START) 100% (we have ALL of it!) 120 g (given in problem) 0 (no time has gone by) 120/2 = 60 1 0 + 3.053 = 3.053 100% /2 = 50% 3.053 + 3.053 = 6.106 60/2 = 30 50%/2 = 25% 2 30/2 = 15 3 6.106 + 3.053 = 9.159 25%/2 = 12.5% 15/2 = 7.5 4 12.5%/2 = 6.25% 9.159 + 3.053 = 12.212

  22. EXAMPLE: What is the half-life of a 100.0 g sample of nitrogen-16 that decays to 12.5 g of nitrogen-16 in 21.6 s? • To get to 12.5 g, it takes 3 half lives. The time is 21.6 s. • Take the time and divide it by the number of half lives to determine how long one half life is. • 21.6 s / 3 half lives = • Check your work by filling in the rest of the table 7.2 s for each half life 100 g (given in problem) 100% (we have ALL of it!) 0 (START) 0 (no time has gone by) 1 50 g 50% (1/2) 7.2 2 25 g 25% (1/4) 14.4 3 12.5 g (stop) 12.5% (1/8) 21.6 (given in problem)

  23. Homework • Part 3 of HW pkt

  24. December 8, 2016 • Half-Life Lab

  25. December 9, 2016 Announcements Check homework packet 1-4 Notes Quizlet up today Do not forget U of T due Friday

  26. Goals • To explain fusion and fission • To describe the three types of radioactive decay • To describe benefits and drawbacks of nuclear energy

  27. What are the three types of radioactive decay? • Alpha • Structure: 2 protons and 2 neutrons • Symbol: He • When alpha particle is given off: • Mass number: -4 • Atomic number: -2 4 2

  28. What are the three types of radioactive decay? 2. Beta • Structure: neutron is changed into a proton and electron; the electron is then given off • Symbol: e • When beta decay occurs: • Mass number: no change • Atomic number: +1 0 -1

  29. What are the three types of radioactive decay? 3. Positron Emission (Beta Capture) • Structure: particle similar to e- in mass, but positive charge • Symbol: e • When positron emission occurs: • Mass number: no change • Atomic number: -1 0 +1

  30. Gamma (Most dangerous to humans) - occurs when nucleus has too much energy, so it “settles down” - when it settles, it releases energy in the form of a PHOTON

  31. Notes: Benefits • Not a lot of materials to start reaction that gives off a lot of energy, so cheaper • Materials last a while • Clean waste products (water vapor is all that’s released to air) • Others?

  32. Notes: Drawbacks • Dangerous (Chernobyl, Three Mile Island) • Radioactive wastes • Others?

  33. Homework • Complete Part 5 and 6 of homework packet

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