Nuclear Chemistry Proposal: build a nuclear power plant in Broome County. List the pros & cons 1
Nuclear Chemistry Friend or Fiend 2
The Nucleus What is in the nucleus? How big is it vs. the atom? How was it discovered? 3
Isotope Notation (protons & neutrons in nucleus) mass # (p+n) p atomic # X 14 6 C X -(p+n) C -14 4
Notation: Try It How many p, n, and e -? 238 92 U Pb -210 What is the nuclear charge of Br? What is the charge of the bromide ion? What is the difference between mass number and atomic mass? 5
Types of Radiation Unstable nuclei will change (or decay ) by emitting radiation. + b g unstable nuclei - electric field a screen 6
a Radiation 2a 4 high mass high charge Some nuclei eject a positive a (alpha) particle. A piece of paper can stop an a particle. Why is it stopped so easily? What element is a related to? 7
b Radiation Some nuclei eject a fast moving electron or beta particle (b particle). e - 8
g Radiation g g (gamma) radiation is high energy light (electromagnetic radiation) that can easily penetrate wood, bricks, and human tissue. 9
Radiation Damage Type of Radiation a b g Damage to Human Tissue low moderate high 10
Elementary Particles Alpha 4 4 2 He or 2a 0 0 Electron -1 e or b or b- -1 Gamma Neutron Proton 0 0g 1 0 n 1 1 p or 1 1 H 0 0 Positron 1 e or b or b+ 1 11
Electron vs. Beta (Identical) From atomic orbit 0 0-1 e or b or -1 b- Ejected from nucleus 12
Balancing Nuclear Reactions 1.Mass number of products & reactants are equal. (superscripts balance) 2.Charge of products & reactants are equal (subscripts balance) 13
Balancing Nuclear Reactions 212 84 Po 208 82 Pb + X 137 55 Cs 137 56 Ba + X 14
Balancing Nuclear Reactions 78 As -1e 0 + X 33 14 7 N + 1 0n 14 6 C + X 15
Try Another! Write a balanced nuclear equation for the decay of Ra-226 to produce an isotope of radon (Rn) and an alpha particle. 16
Transmutation Conversion of one element into another 1. Natural Transmutation 2. Artificial Transmutation (man-made) 17
Natural Transmutation An unstable nucleus changes into another element by emitting a particle in a process called radioactive decay. AB particle and/or g radiation (light) 18
What Holds a Nucleus Together? charge repulsion of protons strong force vs nucleus flies apart holds nucleus together 19
Nuclear Stability Over 1500 isotopes (nuclei) are known, but only 264 are stable. 20
Number of n 40 80 120 Belt of Stability #p = #n 20 40 60 80 Number of p 21
Stable Nuclei n p 1.Low atomic number: #n = #p e.g. C-12, N-14, O-16 2.High atomic number: #n > #p e.g. Pb-206 (82 p & 124 n) 3.All nuclei with atomic number > 82 are unstable (too many p & n) 22
Number of n 40 80 120 Belt of Stability C > Pb Isotope mass > PT atomic mass b - emission A B Isotope mass < PT atomic mass b + emission 20 40 60 80 Number of p a emission At. mass on PT is a guide to stability 23
Region A Isotope mass greater than atomic mass on P.T. results in b - emission 1 0 n 1 1 p + 0-1 e b - emission 42 K 19 42 20 Ca + 0-1 e greater than P.T. (39 amu) 24
Region B Isotope mass less than atomic mass on P.T. results in b + emission 1 1 1 p 0 n + 0 1 e b + 37 K 19 37 18 Ar + 0 1 e emission less than P.T. (39 amu) 25
Region C For nuclei past lead (Pb) alpha emission reduces both n & p. 238 92 U 234 90 Th + 2a 4 Past Pb on P.T. 26
Nuclear Stability: Summary Atomic numbers 1-82 Region A: too many n mass # > PT mass B: too few n mass # < PT mass Emission beta b - positron b+ Atomic number >82 C: too many p & n alpha a 27
Using Table N Table N shows the natural transmutation of several nuclides. Write balanced equations for the decay of: N-16 Rn-222 28
Predict the Reaction Check Table N first. If not on N, use rules of stability. Write the decay reaction of: Cu-66 Ti-45 Pu-239 C-14 29
Radioactive Decay Series Sequence of nuclear reactions leading to stable isotope. 30
Radioactive Decay Series e.g. Still not stable 238 92 U 234 90 Th + 4 2a parent daughter Final stable daughter: 206 82 Pb31
Radioactive Half-Life Half-life (T ½ ): time for one-half of the radioactive atoms to decay into products. You don t know when an individual isotope will decay! Long T ½ relatively stable isotope 32
% remaining Half-Life Decay initial 100 50 1 half-life 2 half-lives 3 half-lives 25 0 0 1 2 3 half-lives 33
Solving Half-Life Problems elapsed time = half-life periods T ½ Example: If T ½ = 7.2 s and elapsed time = 28.8 s, then 28.8 s 7.2 s = 4 half-life periods 34
Half-Life: Loop Method How much of a 50.g sample of K-42 remains after 37.2 h? Table N shows half-life is 12.4 h. 50. g 37.2 h 12.4 h = 3 half-life periods (3 loops) 25 g 12.5 g 6.25 g 1 half-life 2 half-life 6.25 g remains. 3 half-life 35
Half-Life Problem You start with 68 g of C-14 Write a balanced equation for its decay. How long is 3 half-life periods? How many grams of C-14 remain after 3 half lives? 36
Half-Life Problem What percent of I-131will remain after 40.1 days? What fraction of I-131will remain after 24.1 days? 37
Alchemist s Dream 38
Artificial Transmutation Bombard a nucleus with a particle to form a new element. Rutherford 1919: discovered proton. Alpha injected into nucleus with particle accelerator. 14 4 1 7 N + 2a 17 8 O + 1 p 2 reactants = artificial trans. can t predict both products 39
Artificial Transmutation Chadwick 1932: discovered the neutron: 9 4 Be + 2a 4 12 6 C + 1 0 n Why was detecting the neutron so difficult? 40
Artificial Transmutation All elements with Z > 92 (transuranium elements) were produced by transmutation. 238 92 U + 1 0 n 239 93 Np + 0-1 e Artificial or man-made 41
Uses of Radioisotopes Radioactive dating Radioactive tracers (read p.860) Medical applications Nuclear power 42
Radioactive Dating: C-14 C-12 >99% stable C-14 <1% unstable After the plant dies, only C-14 decays. The ratio of C-14 to C-12 can tell the age since death. 43
14 Radioactive Dating 6 C 14 7 N + -1 b T ½ = 5715 yr Dates living things up to ~40,000 yr 238 92 U 206 82 Pb + 6 0-1 b + 8 4 2a T = 4.47 x 10 9 yr ½ 0 Dates rocks billions of years. Does this equation balance? 44
Radioactive Dating 45
Medical Applications Iodine-131 for treatment of thyroid cancer. (injested, so need short T ½ ) Cobalt-60, a gamma ray emitter for treating cancer. Tc-99 for treatment of cancer. 46
Nuclear Power Fission- splitting heavy nuclei Fusion- combining light nuclei 47
Fission & Fusion Mass of products is less than mass of reactants. Mass is lost!!! E = mc 2 energy produced missing mass speed of light 3 x 10 8 m/s 48
Nuclear Fission Splitting a large nucleus into smaller isotopes, releasing energy. Used in nuclear power plants 49
Nuclear Power Plant U-235, hit by a n o, splits into smaller nuclei & 3 n o & energy. 235 U+ 1 92 0 n 90 38 Sr+ 143 Xe+ 3 1 0n 54 chain reaction n o U-235 50
Nuclear Fusion Small nuclei combine (unite) to form a larger nucleus and release energy. Required very high temps. (40,000,000 o C) Why? Energy from the sun is produced by fusion. 51
Solar Fusion Hydrogen nuclei fuse into helium. 1 4 H + 2-1e 0 4 He + energy 1 2 E = mc 2 52
Detecting Radiation Your senses cannot detect radiation. Geiger counter- b radiation Scintillation counter- all types of radiation Film badge-all types of radiation 53
Reactions: Chemical Atoms rearranged Involves only electrons Small DE Nuclear Elements changed Involves all atomic particles Large DE Rate depends on T, P, etc. Rate is constant 54
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Warm-up What are the three types of radiation (names and symbols). Which is most and least damaging radiation to humans? How many p +, n, e - in Es-252 56
Warm-up How many p +, n, e - in titanium-48? What is the nuclear charge of this isotope? Write a balance equation for carbon-14 emitting a beta particle. 57
Warm-up Write a balanced equations for the radioactive decay: Neon-19 Bromine-81 Neptunium-237 58
Warm-up Write an equation for the decay of: technetium-99 silicon-26 californium-252 Use Table N or compare mass number vs. atomic mass. 59
Warm-up 235 92 90 U+ X 38 Sr+ 143 Xe+3 1 54 0 n What is X? 60
Warm-up 87.5% of an isotope decays in 4.8 days. What is its half-life? Careful! 61
Warm-up Write an equation for the decay of O-19, with a half-life of 29 s. If you start with 120 g of O-19, how much remains after 116 s? How long will it take for a sample of O-19 to drop to one-eighth of its original amount? 62
Warm-up If aluminum-27 is bombarded with an alpha particle, one of the products is silicon-30. What is this process called? Write a balanced equation. 14.0 g of Co-60 remains after 21 yr. What was the original sample size? Write an equation for the decay of Fe-53. What is this process called? 63