1 nuclear chemistry. 2 radioactivity emission of subatomic particles or high- energy electromagnetic...

Download 1 Nuclear Chemistry. 2 Radioactivity Emission of subatomic particles or high- energy electromagnetic radiation by nuclei Emission of subatomic particles

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  • Slide 1
  • 1 Nuclear Chemistry
  • Slide 2
  • 2 Radioactivity Emission of subatomic particles or high- energy electromagnetic radiation by nuclei Emission of subatomic particles or high- energy electromagnetic radiation by nuclei Such atoms/isotopes said to be radioactive Such atoms/isotopes said to be radioactive
  • Slide 3
  • 3 Its discovery Discovered in 1896 by Becquerel Discovered in 1896 by Becquerel Called strange, new emission uranic rays Called strange, new emission uranic rays Cuz emitted from uranium Cuz emitted from uranium Marie Curie & hubby discovered two new elements, both of which emitted uranic rays Marie Curie & hubby discovered two new elements, both of which emitted uranic rays Polonium & Radium Polonium & Radium Uranic rays became radioactivity Uranic rays became radioactivity
  • Slide 4
  • 4
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  • 5 Types of radioactivity Rutherford and Curie found that emissions produced by nuclei Rutherford and Curie found that emissions produced by nuclei Different types: Different types: Alpha decay Alpha decay Beta decay Beta decay Gamma ray emission Gamma ray emission
  • Slide 6
  • 6 Isotopic symbolism Lets briefly go over it Lets briefly go over it Proton = 1 1 p Proton = 1 1 p Neutron = 1 0 n Neutron = 1 0 n Electron = 0 -1 e Electron = 0 -1 e
  • Slide 7
  • 7 Types of decay: alpha decay Alpha ( ) particle: helium-4 bereft of 2e - Alpha ( ) particle: helium-4 bereft of 2e - = 4 2 He = 4 2 He Parent nuclide daughter nuclide + He-4 Parent nuclide daughter nuclide + He-4 238 92 U 234 90 Th + 4 2 He Daughter nuclide = parent nuclide atomic # minus 2 Daughter nuclide = parent nuclide atomic # minus 2 Sum of atomic #s & mass #s must be = on both sides of nuclear equation! Sum of atomic #s & mass #s must be = on both sides of nuclear equation!
  • Slide 8
  • 8
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  • 9 Alpha decay Has largest ionizing power Has largest ionizing power = ability to ionize molecules & atoms due to largeness of -particle = ability to ionize molecules & atoms due to largeness of -particle But has lowest penetrating power But has lowest penetrating power = ability to penetrate matter = ability to penetrate matter Skin, even air, protect against -particle radiation Skin, even air, protect against -particle radiation
  • Slide 10
  • 10 Beta decay Beta ( ) particle = e - Beta ( ) particle = e - How does nucleus emit an e - ? How does nucleus emit an e - ? neutron changes into proton & emits e - neutron changes into proton & emits e - 1 0 n 1 1 p + 0 -1 e 1 0 n 1 1 p + 0 -1 e Daughter nuclide = parent nuclide atomic number plus 1 Daughter nuclide = parent nuclide atomic number plus 1 137 55 Cs 137 56 Ba + 0 -1 e -
  • Slide 11
  • 11 Beta decay Lower ionizing power than alpha particle Lower ionizing power than alpha particle But higher penetration power But higher penetration power Requires sheet of metal or thick piece of wood to arrest penetration Requires sheet of metal or thick piece of wood to arrest penetration more damage outside of body, but less in (alpha particle is opposite) more damage outside of body, but less in (alpha particle is opposite)
  • Slide 12
  • 12
  • Slide 13
  • 13 Gamma ray emission Electromagnetic radiation Electromagnetic radiation High-energy photons High-energy photons 0 0 0 0 No charge, no mass No charge, no mass Usually emitted in conjunction with other radiation types Usually emitted in conjunction with other radiation types Lowest ionizing power, highest penetrating power requires several inches lead shielding Lowest ionizing power, highest penetrating power requires several inches lead shielding
  • Slide 14
  • 14 Problems Write a nuclear equation for each of the following: Write a nuclear equation for each of the following: 1. beta decay in Bk-249 2. alpha decay of Ra-224
  • Slide 15
  • 15 Cont. In determining nuclear stability, ratio of neutrons to protons (N/Z) important In determining nuclear stability, ratio of neutrons to protons (N/Z) important Notice lower part of valley (N/Z = 1) Notice lower part of valley (N/Z = 1) Bi last stable (non- radioactive) isotopes Bi last stable (non- radioactive) isotopes N/Z too high: above valley, too many n, convert n to p, beta-decay N/Z too high: above valley, too many n, convert n to p, beta-decay N/Z too low: below valley, too many p, convert p to n N/Z too low: below valley, too many p, convert p to n
  • Slide 16
  • 16 Magic numbers Actual # of n & p affects nuclear stability Actual # of n & p affects nuclear stability Even #s of both n & p give stability Even #s of both n & p give stability Similar to noble gas electron configurations: 2, 10, 18, 36, etc. Similar to noble gas electron configurations: 2, 10, 18, 36, etc. Since nucleons (= n+p) occupy energy levels within nucleus Since nucleons (= n+p) occupy energy levels within nucleus N or Z = 2, 8, 20, 28, 50, 82, and N = 126 N or Z = 2, 8, 20, 28, 50, 82, and N = 126 Magic numbers Magic numbers
  • Slide 17
  • 17 Radioactive decay series
  • Slide 18
  • 18 Detecting radioactivity Particles detected through interactions w/atoms or molecules Particles detected through interactions w/atoms or molecules Simplest film-badge dosimeter Simplest film-badge dosimeter Photographic film in small case, pinned to clothing Photographic film in small case, pinned to clothing Monitors exposure Monitors exposure Greater exposure of film greater exposure to radioactivity Greater exposure of film greater exposure to radioactivity
  • Slide 19
  • 19 Geiger counter Emitted particles pass through Ar-filled chamber Emitted particles pass through Ar-filled chamber Create trail of ionized Ar atoms Create trail of ionized Ar atoms Induced electric signal detected on meter and then clicks Induced electric signal detected on meter and then clicks Each click = particle passing through gas chamber Each click = particle passing through gas chamber
  • Slide 20
  • 20 Radioactive decay kinetics Half-life = time taken for of parent nuclides to decay to daughter nuclides Half-life = time taken for of parent nuclides to decay to daughter nuclides
  • Slide 21
  • 21 Radiometric dating: radiocarbon dating Devised in 1949 by Libby at U of Chicago Devised in 1949 by Libby at U of Chicago Age of artifacts, etc., revealed by presence of C-14 Age of artifacts, etc., revealed by presence of C-14 C-14 formed in upper atmosphere via: C-14 formed in upper atmosphere via: 14 7 N + 1 0 n 14 6 C + 1 1 H 14 7 N + 1 0 n 14 6 C + 1 1 H C-14 then decays back to N by - emission: C-14 then decays back to N by - emission: 14 6 C 14 7 N + 0 -1 e; t 1/2 = 5730 years 14 6 C 14 7 N + 0 -1 e; t 1/2 = 5730 years Approximately constant supply of C- 14 Approximately constant supply of C- 14 Taken up by plants via 14 CO 2 & later incorporated in animals Taken up by plants via 14 CO 2 & later incorporated in animals Living organisms have same ratio of C-14:C-12 Living organisms have same ratio of C-14:C-12 Once dead, no longer incorporating C-14 ratio decreases Once dead, no longer incorporating C-14 ratio decreases 5% deviation due to variance of atmospheric C-14 5% deviation due to variance of atmospheric C-14 Bristlecone pine used to calibrate data Bristlecone pine used to calibrate data Carbon-dating good for 50,000 years Carbon-dating good for 50,000 years
  • Slide 22
  • 22 Radiometric dating: uranium/lead dating Relies on ratio of U-238:Pb-206 w/in igneous rocks (rocks of volcanic origin) Relies on ratio of U-238:Pb-206 w/in igneous rocks (rocks of volcanic origin) Measures time that has passed since rock solidified Measures time that has passed since rock solidified t 1/2 = 4.5 x 10 9 years t 1/2 = 4.5 x 10 9 years For ex, if rock contains equal amts of isotopes above, it would be 4.5 billion years old For ex, if rock contains equal amts of isotopes above, it would be 4.5 billion years old
  • Slide 23
  • 23 Fission Meitner, Strassmann, and Hahn discovered fission: splitting of uranium-235 Meitner, Strassmann, and Hahn discovered fission: splitting of uranium-235 Instead of making heavier elements, created a Ba and Kr isotope plus 3 neutrons and a lot of energy Instead of making heavier elements, created a Ba and Kr isotope plus 3 neutrons and a lot of energy Sample rich in U-235 could create a chain rxn Sample rich in U-235 could create a chain rxn To make a bomb, however, need critical mass = enough mass of U-235 to produce a self-sustaining rxn To make a bomb, however, need critical mass = enough mass of U-235 to produce a self-sustaining rxn
  • Slide 24
  • 24 Nuclear power In America, about 20% electricity generated by nuclear fission In America, about 20% electricity generated by nuclear fission Imagine: Imagine: Nuclear-powered car Nuclear-powered car Fuel = pencil-sized U-cylinder Fuel = pencil-sized U-cylinder Energy = 1000 20-gallon tanks of gasoline Energy = 1000 20-gallon tanks of gasoline Refuel every 1000 weeks (about 20 years) Refuel every 1000 weeks (about 20 years)
  • Slide 25
  • 25 Nuclear power plant Controlled fission through U fuel rods (3.5% U-235) Controlled fission through U fuel rods (3.5% U-235) Rods absorb neutrons Rods absorb neutrons Retractable Retractable Heat boils water, making steam, turning turbine on gener

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