Nuclear Chemistry

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Nuclear Chemistry

  1. 1. Nuclear Chemistry
  2. 2. Radioactivity <ul><li>There are two main types of radioactivity: Natural and Induced </li></ul>
  3. 3. Natural Radioactivity <ul><li>Occurs in nature </li></ul><ul><li>Usually large, unstable nuclei </li></ul><ul><li>Occurs in three ways: </li></ul><ul><ul><li> Particle (alpha particle) </li></ul></ul><ul><ul><li> Particle (beta particle) </li></ul></ul><ul><ul><li> Ray (gamma ray) </li></ul></ul>
  4. 4. Alpha Decay <ul><li>A helium nucleus is released from the nucleus. ( ) </li></ul><ul><ul><li>The mass decreases by 4 </li></ul></ul><ul><ul><li>The atomic number decreases by 2 </li></ul></ul><ul><ul><li>(Because the He nucleus has 2p + and 2n o ) </li></ul></ul><ul><li>Alpha radiation can be stopped by a piece of paper. Cannot penetrate skin. Not dangerous. </li></ul>
  5. 5. Alpha Decay Example Notice that the uranium has changed into a new element, thorium.
  6. 6. Beta Decay <ul><li>An electron is released from the nucleus when a neutron becomes a proton. </li></ul><ul><li>The mass is unaffected. (the mass of a neutron is roughly equal to the mass of a proton) </li></ul><ul><li>The atomic number is increased by 1. </li></ul><ul><li>Harder to stop and more dangerous. </li></ul>
  7. 7. Beta Decay Example Notice that carbon has changed into nitrogen.
  8. 8. Gamma Decay <ul><li>Pure energy is released from the nucleus. </li></ul><ul><li>The mass and atomic number are unaffected. </li></ul><ul><li>Stopped by lead. The most harmful to living tissue. </li></ul>
  9. 9. Gamma Decay Example No new element formed. Gamma radiation (energy) released.
  10. 10. Induced Radioactivity <ul><li>Particles are slammed together to cause transmutation of stable elements. (Nuclear Bombardment) </li></ul><ul><li>Discovered by Rutherford in 1919. </li></ul>
  11. 11. Uranium-238 Decay Series
  12. 12. Radioactive Decay of U-238 <ul><li>Uranium-238 becomes Thorium-234 </li></ul><ul><li>Transmutation by Alpha Decay </li></ul>
  13. 13. Radioactive Decay of U-238 Thorium-234 becomes Protactinium-234 Transmutation by Beta Decay
  14. 14. Radioactive Decay of U-238 Protactinium-234 becomes Uranium-234 Transmutation by Beta Decay
  15. 15. Radioactive Decay of U-238 Uranium-234 becomes Thorium-230 Transmutation by Alpha Decay
  16. 16. Radioactive Decay of U-238 Thorium-230 becomes Radium-226 Transmutation by Alpha Decay
  17. 17. Radioactive Decay of U-238 Radium –226 becomes Radon-222 Transmutation by Alpha Decay
  18. 18. Radioactive Decay of U-238 Radon-222 becomes Polonium-218 Transmutation by Alpha Decay
  19. 19. Radioactive Decay of U-238 Polonium-218 becomes Lead-214 Transmutation by Alpha Decay
  20. 20. Radioactive Decay of U-238 Lead-214 becomes Bismuth-214 Transmutation by Beta Decay
  21. 21. Radioactive Decay of U-238 Bismuth-214 becomes Polonium-214 Transmutation by Beta Decay
  22. 22. Radioactive Decay of U-238 Polonium-214 becomes Lead-210 Transmutation by Alpha Decay
  23. 23. Radioactive Decay of U-238 Lead-210 becomes Bismuth-210 Transmutation by Beta Decay
  24. 24. Radioactive Decay of U-238 Bismuth-210 becomes Polonium-210 Transmutation by Beta Decay
  25. 25. Radioactive Decay of U-238 Polonium-210 becomes Lead-206 Transmutation by Alpha Decay Lead-206 is stable. (phew!)
  26. 26. Half-Life <ul><li>The time it takes for half of the atoms in a given radioactive sample to decay into a more stable isotope. </li></ul><ul><li>This number is different for each kind of isotope of any kind of element. </li></ul><ul><li>Can be calculated because atoms decay at a predictable rate. </li></ul><ul><li>Half lives can range from fractions of a second to millions of years. </li></ul>
  27. 27. Half-Life (n=#cycles) <ul><li>Two formulas will help you solve half life problems: </li></ul><ul><li>1 . Half-Life = Total time </li></ul><ul><ul><li>n </li></ul></ul><ul><ul><li>2. Final Mass = Total Mass </li></ul></ul><ul><ul><li> 2 n </li></ul></ul>
  28. 28. Example Problems <ul><li>The half-life of technetium is 6.00 hours. What mass of Tc-99 remains from a 10.0 gram sample after 24.0 hours. </li></ul><ul><ul><li>Since 24.0 hours is 4 half-life cycles, the original 10.0 gram sample is divided four times. </li></ul></ul><ul><ul><li>Final Mass = Total Mass </li></ul></ul><ul><ul><li> 2 n </li></ul></ul><ul><ul><li>10.0 g = 10.0g = 0.625 g Tc-99 remain </li></ul></ul><ul><ul><li>2 4 16 </li></ul></ul>
  29. 29. How about another one??? <ul><li>A 50.0g sample of N-16 decays to 12.5g in 14.4s. What is its half-life? </li></ul><ul><ul><li>Half-Life = Total Time </li></ul></ul><ul><ul><ul><ul><ul><li> n </li></ul></ul></ul></ul></ul><ul><ul><ul><ul><ul><li>Half-Life = 14.4s </li></ul></ul></ul></ul></ul><ul><ul><ul><ul><ul><li>2 </li></ul></ul></ul></ul></ul><ul><ul><ul><ul><ul><li>Half-Life = 7.2s </li></ul></ul></ul></ul></ul>50.0g 1 half = 25.0g 2 half = 12.5 g
  30. 30. Sure, one more… why not? <ul><li>There are 5.0g of I-131 left after 40.35 days. How many grams were in the original sample if its half-life is 8.07 days? </li></ul><ul><li>Final Mass = Total Mass </li></ul><ul><li> 2 n </li></ul><ul><li>1 st : How many cycles have occurred? </li></ul><ul><li>40.35 / 8.07 = 5 cycles. </li></ul><ul><li>2 nd : Rearrange the formula to solve for the original total mass. </li></ul><ul><li>Total Mass = Final Mass x 2 n </li></ul>
  31. 31. So, solve it already!!! <ul><li>3 rd : Solve </li></ul><ul><li>Total Mass = 5.0g x 2 5 </li></ul><ul><li>Total Mass = 5.0g x 32 </li></ul><ul><li>Total Mass = 160.0g </li></ul>
  32. 32. Shall we check it???(of course) <ul><li>160.0g Total Mass </li></ul><ul><li>At the end of one half life = 80.0g </li></ul><ul><li>(8.07days) </li></ul><ul><li>At the end of two cycles = 40.0g </li></ul><ul><li>(16.14 days) </li></ul><ul><li>At the end of three cycles = 20.0g </li></ul><ul><li>(24.21 days) </li></ul><ul><li>At the end of four cycles = 10.0g </li></ul><ul><li>(32.28 days) </li></ul><ul><li>At the end of five cycles = 5.0g </li></ul><ul><li>(40.35 days) </li></ul>
  33. 33. <ul><li>Since decay occurs at a predictable rate, we can use the ratio of decayed to undecayed isotopes to… </li></ul><ul><li>Determine the age of Organic Matter with Carbon – 14 (Up to 30,000 yrs) </li></ul><ul><li>Determine the age of Rocks (and therefore other earth structures) with Uranium – 238 (Millions of yrs.) </li></ul>Using Radioisotopes
  34. 34. More uses for radioisotopes… <ul><li>Tracers used to detect structure and function of organs (thyroid, gall bladder, GI tract, etc…) </li></ul><ul><li>Can also be used to track movement of silt in rivers and nutrient uptake in plants. </li></ul><ul><li>Cancer treatment </li></ul><ul><li>Food preservation </li></ul><ul><li>Sensors in Smoke Detectors </li></ul><ul><li>Starters in Fluorescent lamps </li></ul><ul><li>Nuclear fuel for power plants </li></ul>
  35. 35. Detection of Radioactivity <ul><li>Detected with a Geiger Counter . (When ions strike the cylinder of the Geiger counter, it emits an audible click.) </li></ul>
  36. 36. Detection of Radiation <ul><li>Dosimeter – measures the total amount of radiation that a person has received. Works because photographic film is sensitive to radiation. Usually is worn like a badge. The film is later developed and the exposure to radiation can be measured. </li></ul><ul><li>Unit used to measure radiation exposure in humans is the rem . (Stands for R oentgen E quivalent for M an) Roentgen discovered X-rays. </li></ul>
  37. 37. Biological Effects of Radiation <ul><li>Destruction of tissue especially blood and lymph which cells multiply rapidly. </li></ul><ul><li>Causes various cancers. </li></ul><ul><li>Direct damage to an organism is called Somatic Damage . </li></ul><ul><li>Damage that affects reproductive cells is called Genetic Damage . This leads to birth defects in offspring. </li></ul>
  38. 38. Nuclear Fission <ul><li>A large nucleus is split into two smaller nuclei of approximately equal mass. </li></ul><ul><li>The fission of 4.5g of U-235 will satisfy the average person’s energy needs for an entire year. (Equal to about 15 tons of coal.) </li></ul>
  39. 39. Nuclear Fission <ul><li>The total mass of the products in a fission reaction is slightly less than the mass of the starting materials. </li></ul><ul><li>Law of Conservation of Matter does not apply to fission reactions! </li></ul><ul><li>This small amount of “missing” mass is converted into a huge amount of energy. (E = mc 2 ) c=300,000,000m/s </li></ul>
  40. 40. Nuclear Fission <ul><li>A fission reaction can produce a Chain Reaction because each reaction releases high speed neutrons, each capable of starting another fission reaction. </li></ul><ul><li>Chain reactions make the fission process sustainable for use in Nuclear Power Plants. </li></ul>
  41. 41. Nuclear Fusion <ul><li>Two small nuclei join to form a large nucleus. </li></ul><ul><li>Some mass is converted into energy (even more than fission reactions) </li></ul><ul><li>Difficult to produce and control. To overcome the repulsion between nuclei, they must be heated to 40 million kelvins. For this reason, they are sometimes called Thermonuclear Reactions. </li></ul>
  42. 42. Nuclear Fusion <ul><li>Thermonuclear reactions create the energy produced by the sun and other stars. </li></ul><ul><li>Thermonuclear reactions are the source of the destructive power of a hydrogen bomb. </li></ul><ul><li>Not (yet?) sustainable for use in nuclear power plants. </li></ul>

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