Nuclear Chemistry

1. Nuclear Chemistry Chapter 18

2. Next Generation Science Standards Developrepresentations of the changes in the composition of the nucleus of the atom and the energy released during the processes of fission, fusion, and radioactive decay. Evaluatethe benefits and drawbacks of nuclear processes compared to other types of energy production.

3. Where does our electricity come from? Where are the power stations in CA? • Red dot = fossil fuel burning • Blue = hydroelectric (why there?)

4. Burns fossil fuels: Coal Oil (hydrocarbon) Natural gas (methane) (CH4) Why are they called fossil fuels? 250+ mya Conventional Power Station

5. Conventional Power Station

6. Where are the nuclear power stations in CA? • Diablo Canyon, SLO County • San Onofre, SD County

7. Burns fossil fuels (coal, oil, natural gas) Chemical energy (fossil fuel)  Heat energy (steam)  Kinetic energy (turbine)  Electrical energy (turbine)  your home Conventional Power Station

8. Nuclear Power Station PhET sim: nuclear fission

9. Review: Isotopes p. 642 “Atoms of the same element……. with the same number of protons…… but different numbers of neutrons.” e.g. • H-1 & H-2 • C-12 & C-14 • U-235 & U-238

10. Nuclear power station Notes: “fissionreactionscanproducealargeamountofenergyforexamplethefissionof1gramof uranium-235 generatesasmuchenergyasthecombustionof2700kilogramsofcoalfissionreactionsareusedtogenerateelectricalenergyinnuclearpowerplantsuranium-235 andplutonium-239arethemainradioactiveisotopesusedinnuclearreactors”

11. Nuclear power station p. 655, see fig 12 Fission reactions can produce a large amount of energy. For example the fission of 1 gram of uranium-235 generates as much energy as the combustion of 2700 kilograms of coal. Fission reactions are used to generate electrical energy in nuclear power plants. Uranium-235 and plutonium-239 are the main radioactive isotopes used in nuclear reactors”

12. WARNING: THE LAWS OF CHEMISTRY BREAK DOWN WHEN WE DELVE INTO THE NUCLEUS!!!!! Law of Conservation of Energy Energy can neither be created or destroyed Law of Conservation of Mass Mass can neither be created or destroyed

13. 18.1 ‘Strong Force’ Why doesn’t a nucleus just fly apart? since it is made of protons, and like charges repel each other? What is it that holds a nucleus together? THE STRONG NUCLEAR FORCE p. 643 Teacher notes: youtube: Quarks

14. 18.1 Mass Defect p. 644 • A nucleus weighs slightly less than the particles from which it is made. Uh? See p. 644 fig 4

15. 18.1 Mass defect Imagine assembling the parts of a body….. 1 head (10 lbs) + 1 torso (40 lbs) + 2 arms (10 lbs each) + 2 legs (10 lbs each) = 90 lbs But when we put it all together it only weighs 89 lbs!!!!!!!!!!!

16. 18.1 Mass Defect Mass defect is the difference in mass between a nucleus and the particles from which is made

17. 18.1 Mass Defect p. 644 • The missing mass (m) is converted to energy (E) per Einstein’s equation E = mc2 (c = speed of light = 3 x 108 m/s) • This energy is the binding energy that holds the particles of the nucleus together.

18. 18.1 Nuclear Binding Energy p. 645

19. 18.1 Graph of neutron to proton ratio

20. WARNING: THE LAWS OF CHEMISTRY BREAK DOWN WHEN WE DELVE INTO THE NUCLEUS!!!!!

21. Gamma Radiation

22. Gamma radiation is a type of electromagnetic wave Very high frequency/ low wavelength High energy Penetrating power: stopped by several cm of lead Gamma Radiation

23. 18.2 Radioactivity • Small nuclei • n : p = • 1 : 1 • Large nuclei • n : p • 1.5 : 1

24. 18.2 Alpha Decay Penetrating power: stopped by a layer of skin or a sheet of paper Am-241 Half-life = 470 years

25. Practice problems Nuclear equations must be balanced: See p. 652 Write the nuclear equation for the radioactive decay of Rn-222 by alpha particle emission

26. Radioactive decay sequence

27. 18.2 Beta Decay A neutron is converted into a proton and an electron The electron shoots out the nucleus (called a beta particle). Penetrating Power: stopped by a few sheets of Aluminum foil

28. Practice problems • Write the nuclear equation for the radioactive decay of Rb-87 by beta particle emission 2) Write the balanced nuclear equation for the beta decay of K-40 HONS: Calculate the n:p ratios of reactants and products (3 sig figs)*

29. 18.2 Radioactivity Some nuclei are unstable because of their neutron:proton ratio. They become more stable by undergoing a nuclear reaction (radioactive decay)

30. Balancing Nuclear Equations 5a) Calculate the number of neutrons in Rn-222, C-14, Ne-19 Calculate the neutron to proton ratio for Rn-222, C-14, Ne-19

31. Practice problems Scratch paper work: p. 670 #30 p. 671 # 54 # 58 #61

32. Nuclear Transmutation IntheMiddleAges,manyearlychemiststriedtochange,ortransmute,ordinarymetalsinto gold.

33. Nuclear Transmutation In the Middle Ages, many early chemists tried to change, or transmute, ordinary metals into gold. ‘alchemist’ Thesealchemistsdidnotrealizethattransmutation,whereoneelementturnsintoanother,isanuclearreaction.

34. Nuclear Transmutation These alchemists did not realize that transmutation, where one element turns into another, is a nuclear reaction. Transmutationchangesthenucleusofanatomandthereforecannotbeachievedbyordinarychemicalmeans.

35. Nuclear Transmutation Transmutation changes the nucleus of an atom and therefore cannot be achieved by ordinary chemical means. Transmutationwasdiscoveredbybombardingvariouselementswithalphaparticles.

36. Nuclear Transmutation Transmutation was discovered by bombarding various elements with alpha particles. Chemistshavesynthesizedmoreelementsthanthe93thatoccurnaturally.

37. Nuclear Transmutation Chemists have synthesized more elements than the 93 that occur naturally. ‘synthetic element’ Alloftheelementswithmorethan92protonsaresyntheticelements.

38. Nuclear Transmutation All of the elements with more than 92 protons are synthetic elements. ‘Transuranium elements’ Tomaketransuraniumelements,scientistsuseparticle accelerators toslamparticlestogetherathighspeed.

39. Nuclear Transmutation To make transuranium elements, scientists use particle accelerators to slam particles together at high speed.

40. Practice problems Scratch paper work: p. 653 #1,2,3 Which ones are nuclear transmutations? # 2,3

41. 18.2 Concept Review: 28. Nuclear fission refers to a nuclear reaction in which a very heavy nucleus splits into two smaller nuclei, each having a higher binding energy per nucleon than the original nucleus. A very small fraction of naturally occurring uranium undergoes spontaneous fission. Most fission reactions are artificially induced by bombarding nuclei with neutrons. A chain reaction is a fission reaction which, once initiated, sustains itself. The smallest mass of a radioactive material needed to sustain a chain reaction is known as the critical mass of the material

42. Frayer: Nuclear Fission Definitions/Facts/Examples/Non-examples • Read p. 654 PhET: nuclear fission

43. Nuclear Chain Reaction Youtube: mouse trap fission\

44. They originally tried to initiate a nuclear chain reaction by firing protons at the U nucleus. It did not work. Instead, they now fire neutrons to initiate a nuclear chain reaction. Why is that better? Nuclear Chain Reaction

45. Critical mass Copy the defn from the text onto the Facts section of your Frayer summarizer. Comparing a large ball to a small ball: Which has a greater surface area : volume? ANS = the small ball If the small ball were uranium, it would have more surface area to lose neutrons out the side…. And therefore the small ball would be less able to sustain a nuclear chain reaction

46. Frayer: Hiroshima • August 6th 1945 • ‘Little Boy’ • aircraft = Enola Gay • Enriched Uranium • 90,000 – 166,000 deaths • Vid: Hiroshima: Dropping the bomb

47. Nuclear Fission-Example:‘Atomic Bomb’ = ‘Nuclear Bomb’

48. Frayer: Manhattan Project • Los Alamos, New Mexico • Uranium Enrichment • Natural Uranium is mostly U-238 • Fission needs U-235 (0.7%) • Trinity Test, July 16th 1945

49. Nagasaki • August 9, 1945 • ‘Fat Man’ • Plutonium • An estimated 40,000 people were killed outright by the bombing at Nagasaki, and a further 25,000 were injured.[5] Thousands more died later from related blast and burn injuries, and hundreds more from radiation illnesses from exposure to the bomb's initial radiation. • Was President Truman correct to drop the bombs on Hiroshima and Nagasaki?

50. Practice Write the balanced nuclear equation for the alpha particle bombardment of plutonium-239. The reaction products include a hydrogen atom and two neutrons.