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Nuclear Chemistry Continued

Nuclear Chemistry Continued. Element Quiz Next Monday. Elements : #1-36, plus Ag, Sn, I, Xe, Cs, Ba, W, Pt, Au, Hg, Pb, Rn, Fr, Ra, Os, Ir. Transmutation : the process where one element changes into an atom of another element . A series of different types of decay.

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Nuclear Chemistry Continued

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  1. Nuclear Chemistry Continued

  2. Element Quiz Next Monday • Elements: #1-36, plus Ag, Sn, I, Xe, Cs, Ba, W, Pt, Au, Hg, Pb, Rn, Fr, Ra, Os, Ir

  3. Transmutation: the process where one element changes into an atom of another element. • A series of different types of decay • Induced transmutation: the artificial production of a nuclear reaction by striking the nuclei with high-velocity charged particles: “bombarding”

  4. Less common types of decay • Positron emission: the emission of a positron from a nucleus. • Positron: a particle with the same mass as an electron but opposite charge. • A proton becomes a neutron and a positron, then the positron is emitted.

  5. Try it out! • Write a balanced nuclear equation for the positron emission of sulfur-31. 31 S → P + β 31 0 16 15 +1

  6. Less common types of decay • Electron capture: the nucleus of an atom takes an electron. • The electron combines with a proton to form a… neutron.

  7. Try it out! • Write a balanced nuclear equation for the electron capture of sulfur-31. 31 S + β→ P 0 31 16 -1 15 NOTICE! Electron capture and positron emission have the same result, both decrease the atomic # by 1 but have no effect on the mass #

  8. Chapter 25: Nuclear Chemistry Half lives

  9. Radioactive Decay Rates • Radioactive decay rates are measured in half-lives. • Half-life: the time required for ½ of a sample of a substance to radioactively decay. • After each half-life, ½ of the original sample remains • The rest becomes other elements

  10. Radioactive Decay Rates

  11. Radioactive Decay Rates • Calculating half-life • A radioactive substance has a half-life of 10 minutes. How many ½ lives are in… • 20 minutes? • 50 minutes? • 100 minutes? 2 5 10

  12. Radioactive Decay Rates total time ½ life # ½ lives = • A radioactive substance has a half-life of 15.2 days. How many ½ lives are in… • 45.6 days? • 76 days? • 91.2 days? 3 half-lives 5 half-lives 6 half-lives

  13. Radioactive Decay Rates total mass 21/2-lives Left over = • Calculating half-life • How much of a 100 g sample is left over after… • 1 half-life? • 3 half-lives? • 5 half-lives? 50 g 12.5 g 3.13 g

  14. Radioactive Decay Rates total mass 21/2-lives • Calculating half-life Left over = • How much of a 33.45 mg sample remains after… • 1 half-life? • 3 half-lives? • 5 half-lives? 16.73 mg 4.18 mg 1.05 mg

  15. Try it out! • 50.0 grams of molybdenum-91 decays for 62.0 minutes. What is the mass of the sample remaining? Its half-life is 15.49 minutes. t t1/2 62.0 min 15.49 min n = = = 4 half lives 50.0 g 2 x 2 x 2 x 2 ( ) = 3.13 g remaining =

  16. Try it out! • Iron-59 is used in medicine to diagnose blood circulation disorders. The half-life of iron-59 is 44.5 days. How much of a 2.000-mg sample will remain after 133.5 days? 133.5 days 44.5 days = 3 half lives 2.000 mg 2 x 2 x 2 ( ) = 0.250 mg remaining =

  17. Calculating Amount of Remaining Isotope • Carbon-14 emits beta radiation and decays with a half-life of 5730 years. Assume you start with a mass of 225 grams of carbon-14. • How long is 3 half lives? • What mass of the sample will remain? 17,190 years 28.1 g

  18. Nuclear Stability

  19. Nuclear Stability • The strong nuclear force: a force that holds subatomic particles extremely close together • Nucleons: a general term for protons & neutrons • Nuclear energy: Energy released by overcoming the strong nuclear force

  20. Nuclear Stability • All elements with atomic number 83 or greater are radioactive • Neutrons are like glue in the nucleus - The stability of a nucleus depends on its neutron-to-proton (n/p) ratio. • Small nuclei: 1/1 ratio = stable • (26 protons max - Iron) • Large nuclei: 1.5/1 ratio = stable

  21. Nuclear Stability Too big • The band of stability: The area on the graph within which all stable nuclei are found. Alpha decay Too many neutrons β decay • If it’s outside this area, it decays to gain stability. Too many protons Positron emission or electron capture

  22. Nuclear Stability • The steps in calculating the neutron-to-proton ratio (the n/p ratio) for lead-206 are shown in this ex)

  23. Calculate the neutron-to-proton ratio for . Try it out! 1.6 What kind of decay is it likely to undergo? Explain. The isotope has too many neutrons - Beta decay decreases the amount of neutrons

  24. Table of Contents Chapter 25: Nuclear Chemistry Fission, Fusion, Nuclear issues

  25. Nuclear Chemistry: Additional Concepts 1. Radiochemical Dating • Nuclear reaction rates remain constant • So…half-lives are constant. • Radiochemical dating: determining the age of an object by measuring a radioisotope.

  26. 2. Nuclear fission • Heavy atoms (mass number > 60) tend to break into smaller atoms, increasing their stability. • Nuclear fission:splitting an atomic nuclei into 2 approximately equal parts. Chain reaction • releases a large amount of energy. • Critical mass: The minimum amount of mass to sustain a chain reaction

  27. Nuclear reactors • Nuclear power plants use the process of nuclear fission to produce heat in nuclear reactors. • The heat is used to generate steam, which is then used to drive turbines that produce electricity. 7/8/10 –US Dept. of Energy announced $18.2 million for education in Nuclear Energy. Understand the pros and cons

  28. Nuclear Chemistry: Additional Concepts Nuclear reactors 2) What controls the temp? How? 1) What is the role of the fuel rods? FISSION → energy Water slows neutrons 3) What keeps the process under control? How? Control rods absorb neutrons

  29. Nuclear Chemistry: Additional Concepts Nuclear reactors • Fissionable uranium(IV) oxide (UO2) is commonly used as fuel in nuclear reactors. • Cadmium and boron are used to keep the fission process under control.

  30. 1 MWh = Energy for 650 houses, per hour. 1 ton of coal = 2.5 MWh

  31. Breeder reactor reactors able to produce more fuel than they use

  32. 2. Nuclear fission • Famous nuclear meltdowns • 3 mile island (1979) – US • Chernobyl (1986) – Ukraine • several human errors & technical malfunctions • Fukushima (2011) – Japan • Following earthquake

  33. Nuclear Power: • 65,100 MW produced per water tower. • US uses 4 GW/yr, from 104 operating units. (100 GW possible). • Upside: most energy produced, produces weapons-grade Pu • Downside: requires U, & produces waste that will be radioactive for 4.5 billion years.

  34. 3. Nuclear fusion • Nuclear fusion: nuclear reaction where small nuclei combine to form larger ones. • release very large amounts of energy • require extremely high temperatures. (also called thermonuclear reactions)

  35. Solar Energy: • Sun = the source of all energy on our planet. • The sun makes ~35,000 times the total energy used by man. • ~1/3 of this energy is either absorbed by the atmosphere or reflected back into space. 40,000 watts of light per sq. in. of its surface, per second.

  36. Comprehension What is the difference between nuclear fusion and nuclear fission? Nuclear fusion is the combining of nuclei to form a single nucleus. Nuclear fission is the splitting of a nucleus into fragments.

  37. Table of Contents Chapter 25: Nuclear Chemistry A bit more info (red is FYI)

  38. Applications and Effects of Nuclear Reactions • Geiger counters, scintillation counters, and film badges: devices used to detect and measure radiation • Geiger counters • use ionizing radiation • produces an electric current in the counter • rate the strength of the radiation on a scale.

  39. Applications and Effects of Nuclear Reactions • With proper safety procedures, radiation can be useful in industry, in scientific experiments, and in medical procedures. • A radiotracer: a radioisotope that emits non-ionizing radiation and is used to signal the presence of an element or of a specific substance. • Radiotracers are used to detect diseases and to analyze complex chemical reactions. • Any exposure to radiation can damage living cells. • Gamma rays are very dangerous because they penetrate tissues and produce unstable and reactive molecules, which can then disrupt the normal functioning of cells. • The amount of radiation the body absorbs (a dose) is measured in units called rads and rems. • Everyone is exposed to radiation, on average 100–300 millirems per year. A dose exceeding 500 rem can be fatal if received in a short amount of time.

  40. Fin du ch 25

  41. Practice Problems • p. 836-837, • Alpha, beta, gamma: #38, 88 • Radioactive decay: #68-72 • Half-Life: #77-79 (tough) • p. 836, #55, 56, 60, 61, 62, 63, 64

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