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Nuclear Chemistry

Nuclear Chemistry. Radioactivity. 1896—Becquerel Accidently discovered radioactivity Uranium in a drawer 1903—Marie (and Pierre) Curie Able to prove rays came from rock Coined the term “radiation” 1903—Nobel Prize —Becquerel & Curies 1911—Nobel Prize —Marie Curie. Radioactivity.

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Nuclear Chemistry

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  1. Nuclear Chemistry

  2. Radioactivity • 1896—Becquerel • Accidently discovered radioactivity • Uranium in a drawer • 1903—Marie (and Pierre) Curie • Able to prove rays came from rock • Coined the term “radiation” • 1903—Nobel Prize —Becquerel & Curies • 1911—Nobel Prize —Marie Curie

  3. Radioactivity Radioactivity the process by which nuclei emit particles and high-energy rays Radiation the particles and high energy rays emitted during radioactivity Nuclear Chemistry the study of radioactivity

  4. One atom transmutates into a different element • Radioactivity caused by unstable nucleus (DECAY) • LARGE amounts of energy emitted • Temperature and pressure DO NOT affect the rate of reaction • Multiple atoms/compounds • Types of atoms never change • Chemical bonding caused by unstable valence e- config. • small amounts of energy (comparatively) • Temp and pressure affect the rate of reaction Nuclear vs. Chemical Reactions

  5. mass # charge (if any) element symbol atomic # 125 – I 53 iodine is now added to salt Goiter due to lack of iodine Complete Atomic Designation …gives very precise info about an atomic particle

  6. 238U 131I 234Th 235U 226Ra 92 88 92 90 53 Nuclear reactions are caused by an unstable nucleus. The nucleus becomes stable through decay. Before we decay, let’s review… 143 92 92 235 Uranium-238 146 92 Thorium-234 144 90 90 234 138 88 88 226 131 53 Iodine-131 Now…Let’s decay…

  7. Radioactive Skittles Radiation You have 3 radioactive skittles in front of you: Red: α rad. Orange: β rad. Yellow: g rad. One must go in your hand, one must go in your pocket, and the last one must be eaten… What arrangement will cause you the least harm???

  8. Murder with Alpha Decay • In November 2006, former Russian agent Alexander Litvinenko was poisoned with radioactive Polonium at a Sushi Bar in England. News Video

  9. Radioactive Decay For nuclear equations, mass (top) and atomic number (bottom) must balance. 234 230 4 alpha (a) decay: U Th + He 92 90 2 (atomic number decreases by two) a-particle (i.e., a He nucleus): massive, slow-moving; stopped by paper or clothing CANNOT penetrate skin

  10. 234 234 0 beta (b) decay: Pa U + e 91 92 –1 (atomic number increases by one) b-particle (i.e., a fast-moving electron): tiny mass blocked by wood or aluminum foil stops~1 cm into body In b-decay, the net effect is that a n0 is converted into a p+ and an e–. The e– is then released… 1 1 0 n p + e 0 1 –1 *NOTE: A neutron is not actually made up of a p+ and an e-, because there are no e- in the nucleus!

  11. emitted when nucleons rearrange into a more stable configuration gamma radiation (g ): consists of high-energy photons can penetrate to internal organs 0 gamma ray: (or just g) g 0 gamma radiation often accompanies other nuclear decay 234 230 4 0 U Th + He + 2 g 92 90 2 0

  12. b, a, -1 e 0 4 He 2 g 0 0 Recap: Types of Radiation Beta Gamma Alpha High energy wave Composition Helium nucleus Electron Symbol Charge 2+ No charge 1- Mass ~ 4 amu 1/1837 amu No mass PenetratingPower Low Very High Moderate

  13. Transmutation Reactions The conversion of an atom from one element to another element • Radioactive decay (emission) • Particles bombarding the nucleus of an atom

  14. Alf-a Decay + Po 218 He 4 214 Pb 84 2 82 + 231 Pa He 4 227 Ac 91 2 89 Write a transmutation equation for the alpha decay of francium-208. + 208 Fr He 4 204 At 87 2 85 Write a transmutation equation for the alpha decay of radon-222. + 222 Rn He 4 218 Po 86 2 84

  15. Beta Emission + Pb 210 e 0 210 Bi 82 -1 83 + 75 Se e 0 75 Br 34 -1 35 Write a transmutation equation for the beta emission of argon-37. + 37 Ar e 0 37 K 18 -1 19 Write a transmutation equation for the beta emission of carbon-14. + 14 C e 0 14 N 6 -1 7

  16. Radioactive materials will continue to decay until they reach a stable material(Usually with an atomic number less than 83.) Stable Isotope

  17. Nuclear Transformations There are two forces at work in the nucleus: • Strong Nuclear Force • All subatomic particles in very close proximity will attract each other (protons and neutrons) • Electromagnetic Repulsions • Particles of similar charges repel each other Neutrons act as “glue” holding the nucleus together. Therefore, there must be a balance between protons and neutrons. An imbalance causes nuclear instability…

  18. Band of Stability Above the belt:Too many n0, not enough p+ Below the belt:Too many p+, not enough n0

  19. Sources of Radiation • 80% from Natural Sources • 20% Man made from x-rays and consumer products

  20. Half-Life Decay (t1/2) The time required for one-half of the nuclei of a radioisotope sample to decay to products a. Independent of T, P, and concentration b. Useful in radioactive dating

  21. Half-lives can be as short as a fraction of a second or billions of years. Different nuclei have different decay patterns, depending on why they are unstable (i.e. too many protons, too many neutrons, )

  22. 5 4 3 1 2 2 1 3 Carbon-14 emits beta radiation and decays with a half-life of 5730y. Assume you start with a mass of 2.00g of carbon-14. a. How long is 3 half-lives? b. How many grams will remain at the end of 3 half lives? c. How many years will it take for only 0.0625g to remain? • t1/2= 5730y, 3(5730y) = 17190y b. 2.00g 1.00g 0.50g 0.25g c. 2.00g 0.50g 1.00g 0.25g 0.0625g 0.125g t1/2= 5730y, 5(5730y) = 28650y

  23. 1 2 3 t½ equation 2.00g 1.00g 0.50g 0.25g 2.00g(1/2)(1/2)(1/2) or 2.00(1/2)3 = 0.25 g mi = initial mass mf = final mass n = # of half lives mi (1/2)n = mf If 150.0 g of a radioactive substance undergoes 25 half lives, how many g will remain? 4.47 x 10 -6 g 150.0 g (1/2)25 =

  24. Detection of Radioactivity photographic film (film badges): cheap, “ballpark quantitative” Geiger counter: ionization of gas produces measurable electric current

  25. 1 n 0 Nuclear Fission Fission is when a BIG nucleus splits. This requires… neutrons! Anywhere from 1-9 n0 are released! Important fissionable nuclei: U-233, U-235, Pu-239 chain reaction: one nuclear reaction leads to one or more others

  26. Uranium consists mainly as U-238 (spent Uranium)

  27. Chain Reaction

  28. critical mass: (contained) the mass of fissionable material required to maintain a chain reaction at a constant rate. (Nuclear Reactor) supercritical mass: (uncontained) the mass above which the chain reaction accelerates safe safe critical mass supercritical mass (reaction maintained at constant rate) Little Boy, later dropped on Hiroshima (“Ah jes’ felt lahk runnING.”) (“Run, Forrest, run!”)

  29. Nuclear Power (controlled)

  30. Nuclear Fusion (video) When two small nuclei collide and “fuse” together to form one nucleus. This results in a LARGE amount of energy This happens at extreme temperatures…like the sun! The search for “cold fusion” is in progress.

  31. Nuclear Fusion -- also called thermonuclear reactions -- products are generally NOT radioactive -- requires high temperatures (> 40,000,000 K) !!!! -- the tokamak uses magnetic fields to contain and heat the reaction

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