Ch 25 notes


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Ch 25 notes

  1. 1. Nuclear Chemistry Ch 4.5 & 25
  2. 2. Nuclear Reactions vs. Normal Chemical Changes <ul><li>Nuclear reactions- reactions that take place inside the nucleus of an atom </li></ul>CHEMICAL REACTIONS NUCLEAR REACTIONS Bonds are broken and formed Nuclei emit particles and/or rays Atoms remain unchanged, only rearranged 2H 2 + O 2  2H 2 O Atoms are changed into other atoms of different elements Involve valence electrons Involves the nucleus, P + , N 0 , e- Small energy changes large energy changes ( BINDING Energy) Rate influenced by conc, temp., pressure and catalyst Not affected by those
  3. 3. Radioactivity <ul><li>One of the pieces of evidence for the fact that atoms are made of smaller particles came from the work of Marie Curie a Polish scientist (1876-1934). </li></ul><ul><li>She discovered radioactivity, the spontaneous disintegration of some elements into smaller pieces (other elements). </li></ul>
  4. 4. Radioactivity <ul><li>Many nuclei are radioactive. </li></ul><ul><li>This means they are unstable and will decay by emitting a particle or ray, transforming the nucleus into another nucleus, or into a lower energy state. </li></ul><ul><li>A chain of decays takes place until a stable nucleus is reached. </li></ul>
  5. 5. Radioactivity & Unstable Atoms <ul><li>If # of neutrons is too high or too low, the nucleus becomes unstable and emits energy. </li></ul><ul><li>Any atom containing an unstable nucleus is called a radioactive isotope or radioisotope </li></ul><ul><ul><ul><ul><li>* **More than 1,500 different </li></ul></ul></ul></ul><ul><ul><ul><ul><li>nuclei are known. Of those, </li></ul></ul></ul></ul><ul><ul><ul><ul><li>only 264 are stable and do </li></ul></ul></ul></ul><ul><ul><ul><ul><li>not decay or change with </li></ul></ul></ul></ul><ul><ul><ul><ul><li>time. These nuclei are in a </li></ul></ul></ul></ul><ul><ul><ul><ul><li>region called the band of </li></ul></ul></ul></ul><ul><ul><ul><ul><li>stability. </li></ul></ul></ul></ul>
  6. 6. Isotopes <ul><li>have the same number of p____, different number of n_____ </li></ul><ul><li>Another way to show an isotope is to have the mass number follow the name of the element (Carbon- 14 or C- 14 ) </li></ul>
  7. 7. Isotopes <ul><li>39 19 K ; 40 19 K 14 6 C ; 12 6 C </li></ul><ul><li>Superscript is the mass number </li></ul><ul><li>Subscript is the atomic number </li></ul>
  8. 8. Types of Nuclear Radiation <ul><li>Alpha 2.Beta 3. Gamma </li></ul>
  9. 9. Alpha Decay <ul><li>Alpha particle —a positively charged particle (helium isotope ) made up of two p+ & two n o </li></ul><ul><li>the least penetrating </li></ul><ul><li>can be stopped by a sheet of paper </li></ul><ul><li>Symbols:  , </li></ul>
  10. 10. Alpha Decay <ul><li>An alpha particle looks like a helium atom ( 4 2 He)  </li></ul><ul><li>mass reduces by 4 ,the atomic # reduces by 2 </li></ul><ul><li>Examples: </li></ul><ul><li>238 92 U  234 90 Th + 4 2 He </li></ul><ul><li>209 84 Po  205 82 Pb + 4 2 He </li></ul>Parent cell Daughter cell
  11. 11. Beta Decay <ul><li>A beta particle is an e- emitted by an unstable nucleus </li></ul><ul><li>can be stopped by a thin sheet of metal such as aluminum </li></ul><ul><li>Symbols:  , </li></ul>
  12. 12. Beta Decay <ul><li>A beta particle is written 0 -1 e (  ) </li></ul><ul><li>mass remains the same & the atomic # increases by one </li></ul><ul><li>Examples: </li></ul><ul><li>214 82 Pb  214 83 Bi + 0 -1 e </li></ul><ul><li>218 84 Po  218 85 At + 0 -1 e </li></ul>
  13. 13. Gamma decay <ul><li>A gamma ray is a penetrating ray of energy (photon) emitted by an unstable nucleus </li></ul><ul><li>Gamma rays are energy waves that travel through space at the speed of light </li></ul><ul><li>Symbols:  , </li></ul>
  14. 14. Gamma decay (  ) <ul><li>atomic # and mass remain the same, but the energy of nucleus decreases </li></ul><ul><li>Gamma rays are often emitted along with alpha &/or beta particles </li></ul><ul><li>Gamma rays can be stopped by several centimeters of lead or by several meters of concrete </li></ul>
  15. 15. Penetrating Ability
  16. 16. Other Nuclear Particles <ul><li>Neutron </li></ul><ul><li>Positron – a positive electron </li></ul><ul><li>Proton – usually referred to as hydrogen-1 </li></ul><ul><li>Any other elemental isotope </li></ul>
  17. 17. Balancing Nuclear Reactions <ul><li>In the reactants (starting materials – on the left side of an equation) and products (final products – on the right side of an equation) </li></ul><ul><li>Atomic numbers must balance </li></ul><ul><li>and </li></ul><ul><li>Mass numbers must balance </li></ul><ul><li>Use a particle or isotope to fill in the missing protons and neutrons </li></ul>
  18. 18. <ul><li>Nuclear Reactions </li></ul><ul><li>Reactions that occur </li></ul><ul><li>naturally as nuclei </li></ul><ul><li>strive to be stable. </li></ul>
  19. 19. Learning Check <ul><li>What radioactive isotope is produced in the following bombardment of boron? </li></ul><ul><li>10 B + 4 He ? + 1 n </li></ul><ul><li>5 2 0 </li></ul>
  20. 20. Learning Check <ul><li>What radioactive isotope is produced in the following bombardment of boron? </li></ul><ul><li>10 B + 4 He 13 N + 1 n </li></ul><ul><li>5 2 7 0 </li></ul>
  21. 21. Write Nuclear Equations! <ul><li>Write the nuclear equation for the beta emitter Co-60. </li></ul><ul><li>60 Co  60 Ni + 0 e </li></ul><ul><li>27 28 -1 </li></ul>
  22. 22. Half-Life <ul><li>HALF-LIFE is the time that it takes for 1/2 a sample to decompose. </li></ul><ul><li>The rate of a nuclear transformation depends only on the “reactant” concentration. </li></ul><ul><li>Amount remaining = Initial amount x (1/2) t/T </li></ul><ul><li>t/T, where t is the elapsed time and T is the duration of the half-life. </li></ul>
  23. 23. Half-Life Decay of 20.0 mg of 15 O. What remains after 3 half-lives? After 5 half-lives? 2.5mg 0.625mg
  24. 24. Kinetics of Radioactive Decay <ul><li>For each duration (half-life), one half of the substance decomposes. </li></ul><ul><li>For example: Ra-234 has a half-life of 3.6 days If you start with 50 grams of Ra-234 </li></ul>After 3.6 days > 25 grams After 7.2 days > 12.5 grams After 10.8 days > 6.25 grams
  25. 25. Learning Check! <ul><li>The half life of I-123 is 13 hr. How much of a 64 mg sample of I-123 is left after 39 hours? </li></ul>
  26. 26. Detecting Radiation <ul><li>Devices used to detect radiation include Geiger counters & film badges </li></ul>
  27. 27. Radiocarbon Dating <ul><li>Radioactive C-14 is formed in the upper atmosphere by nuclear reactions initiated by neutrons in cosmic radiation </li></ul><ul><li>14 N + 1 o n ---> 14 C + 1 H </li></ul><ul><li>The C-14 is oxidized to CO 2 , which circulates through the biosphere. </li></ul><ul><li>When a plant dies, the C-14 is not replenished. </li></ul><ul><li>But the C-14 continues to decay with t 1/2 = 5730 years. </li></ul><ul><li>Activity of a sample can be used to date the sample. </li></ul>
  28. 28. Limits to Carbon Dating <ul><li>Some organic material must be present and must be from an organism that once lived. </li></ul><ul><li>Cannot reliably detect objects more than 75,000 years old. </li></ul>
  29. 29. Radiation in Real life Radiation Everyday
  30. 30. <ul><li>Fission is the splitting of a nucleus into smaller fragments. Done by Neutron Bombardment </li></ul>Nuclear Fission
  31. 31. A uranium-235 nucleus is struck by a neutron with ordinary thermal energy. An unstable uranium-236 nucleus is formed, but it breaks into two fragments with the release of several neutrons. The neutrons can induce the fission of other uranium-235 nuclei. FISSION
  32. 33. Uranium-235 and Plutonium-239 are the only fissionable isotopes.
  33. 34. FISSION <ul><li>Since the one original neutron causing the reaction has resulted in the production of three neutrons , there is the possibility of a chain reaction occurring. </li></ul><ul><li>A chain </li></ul><ul><li>reaction </li></ul>
  34. 36. Atomic Bombs <ul><li>This is what happens in an atomic bomb. </li></ul><ul><li>A fission bomb uses an uncontrolled nuclear fission chain reaction to release an enormous amount of energy in a small amount of time. </li></ul>
  35. 37. Nuclear Fission & POWER <ul><li>Currently about 103 nuclear power plants in the U.S. and about 435 worldwide. </li></ul><ul><li>17% of the world’s energy comes from nuclear. </li></ul>
  36. 38. Figure 25.11: Diagram of a nuclear power plant. A controlled fission chain reaction.
  37. 39. Fission <ul><li>Advantages: is the lack of air pollution. </li></ul><ul><li>Disadvantages: include the risk of exposure & radioactive waste (takes hundreds of years to decay) </li></ul>Harris plant, near Raleigh Lake Harris
  38. 41. Nuclear Fusion <ul><li>Fusion </li></ul><ul><li>small nuclei combine </li></ul><ul><li>2 H + 3 H 4 He + 1 n + </li></ul><ul><li>1 1 2 0 </li></ul><ul><li>Occurs in the sun and other stars </li></ul>Energy
  39. 42. FUSION <ul><li>Fusion is the name given to the nuclear reaction whereby small nuclei are induced to join together into larger nuclei and release energy in the process. </li></ul><ul><li>It is the reaction that &quot;fuels&quot; all stars including the Sun. </li></ul><ul><li>A typical reaction that is taking place in the Sun is the fusion of two different isotopes of hydrogen to produce helium. </li></ul>
  40. 43. Nuclear Fusion <ul><li>2 1 H + 2 1 H  4 2 He + energy </li></ul><ul><li>Two small, positively-charged nuclei smash together at high temperatures and pressures to form one larger nucleus. </li></ul><ul><li>A small bit of mass is destroyed and converted into a huge amount of energy, more than even fission. </li></ul>
  41. 44. Fusion <ul><li>We do not use fusion reactions for energy b/c of the extremely high temperatures needed to start the reaction & because the plasma would need to be contained. </li></ul>
  42. 45. FISSION AND FUSION <ul><li>Fission is the splitting of an atomic nucleus into two smaller parts </li></ul><ul><li>Fusion is a process in which the nuclei of two atoms combine to form a larger nucleus </li></ul>
  43. 46. Nuclear Medicine: Imaging <ul><li>Thyroid imaging using Iodine-131 </li></ul><ul><li>The radioisotope is used as a tracer. </li></ul><ul><li>Must have a short half-life & can be eliminated from the body quickly. </li></ul>
  44. 47. Food Irradiation <ul><li>Food can be irradiated with  rays from 60 Co or 137 Cs. </li></ul><ul><li>Irradiated milk has a shelf life of 3 mo. without refrigeration. </li></ul><ul><li>USDA has approved irradiation of meats and eggs. </li></ul>“ Radura”  US FDA
  45. 48. Nuclear Music <ul><li>Nuclear Power to the People </li></ul><ul><li>Natural Decay </li></ul><ul><li>One Half Life to Live </li></ul>