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Chapter 4 Nuclear Chemistry: The Heart of Matter Daniel Fraser University of Toledo, Toledo OH ©2004 Prentice Hall Chemistry for Changing Times 10 th edition.

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Presentation on theme: "Chapter 4 Nuclear Chemistry: The Heart of Matter Daniel Fraser University of Toledo, Toledo OH ©2004 Prentice Hall Chemistry for Changing Times 10 th edition."— Presentation transcript:

1 Chapter 4 Nuclear Chemistry: The Heart of Matter Daniel Fraser University of Toledo, Toledo OH ©2004 Prentice Hall Chemistry for Changing Times 10 th edition Hill/Kolb

2 Chapter 42 Types of Radiation Ionizing radiation – knocks electrons out of atoms or groups of atoms –Produces charged species – ions –Charged species that cause damage

3 Chapter 43 Differences Between Chemical and Nuclear Reactions

4 Chapter 44 Half-Life Period for one-half of the original elements to undergo radioactive decay Characteristic for each isotope Fraction remaining = n = number of half-lives

5 Chapter 45 Practice Problems

6 Chapter 46 Radioisotopic Dating Use certain isotopes to estimate the age of various items 235 U half-life = 4.5 billion years –Determine age of rock 3 H half-life = 12.3 years –Used to date aged wines

7 Chapter 47

8 8 Carbon-14 Dating 99.9% 12 C Produce 14 C in upper atmosphere Half-life of 5730 years ~50,000 y maximum age for dating

9 Chapter 49 You obtain a new sample of cobalt-60, half-life 5.25 years, with a mass of 400 mg. How much cobalt-60 remains after years (three half-lives)? Example 4.2 Half-Lives Solution The fraction remaining after three half-lives is 1 2n2n x 2 x === The amount of cobalt-60 remaining is ( ) (400 mg) = 50 mg. 1 8 You have mg of freshly prepared gold-189, half-life 30 min. How much of the gold-189 sample remains after five half-lives? Exercise 4.2A What percentage of the original radioactivity remains after five half-lives? Exercise 4.2B

10 Chapter 410 You obtain a 20.0-mg sample of mercury-190, half-life 20 min. How much of the mercury-190 sample remains after 2 hr? Example 4.3 There are 120 min in 2 hr. There are ( ) = 6 half-lives in 2 hr. The fraction remaining after six half-lives is The amount of mercury-190 remaining is ( ) (20.0 mg) = mg. Solution 1 2n2n x 2 x 2 x 2 x 2 x === A sample of 16.0 mg of nickel-57, half-life 36.0 hr, is produced in a nuclear reactor. How much of the nickel-57 sample remains after 7.5 days? Exercise 4.3A Tc-99 decays to Ru-99 with a half-life of 210,000 years. Starting with 1.0 mg of Tc-99, how long will it take for 0.75 mg of Ru-99 to form? Exercise 4.3B

11 Chapter 411 A piece of fossilized wood has carbon-14 activity one-eighth that of new wood. How old is the artifact? The half-life of carbon-14 is 5730 years. Example 4.4 Solution The carbon-14 has gone through three half-lives: It is therefore about 3 x 5730 = 17,190 years old. 1 8 == x 1 2 x ( ) How old is a piece of cloth that has carbon-14 activity that of new cloth fibers? The half-life of carbon-14 is 5730 years. Exercise

12 Chapter 412 Shroud of Turin Alleged burial shroud of Jesus Christ –Contains faint human likeness –First documented in Middle Ages Carbon-14 dating done in 1988 –Three separate labs –Shroud ~800 years old –Unlikely to be burial shroud

13 Chapter 413 Uses of Radioisotopes Tracers –Easy to detect –Different isotopes have similar chemical and physical properties –Physical, chemical, or biological processes Agriculture – Induce heritable genetic alterations – mutations – Preservative – Destroys microorganisms with little change to taste or appearance of the food

14 Chapter 414 Nuclear Medicine Used for two purposes Therapeutic – treat or cure disease using radiation Diagnostic – obtain information about patients health

15 Chapter 415 Radiation Therapy Radiation most lethal to dividing cells Makes some forms of cancer susceptible Try to destroy cancer cells before too much damage to healthy cells –Direct radiation at cancer cells –Gives rise to side effects

16 Chapter 416 Diagnostic Uses Many different isotopes used –See Table 4.6 Can measure specific things –Iodine-131 to locate tumors in thyroid –Selenium-75 to look at pancreas –Gadolinium-153 to determine bone mineralization

17 Chapter 417 Imaging Positron emission tomography (PET) Uses an isotope that emits a positron Observe amount of radiation released

18 Chapter 418

19 Chapter 419 Penetrating Power of Radiation The more mass the particle has, the less penetrating it is The faster the particle is, the more penetrating it is

20 Chapter 420 Prevent Radiation Damage To minimize damage –Stay a distance from radioactive sources –Use shielding; need more with more penetrating forms of radiation

21 Chapter 421 Energy from Nucleus E = mc 2 Lose mass, gain energy –For chemical reactions, mass changes are not measurable –For nuclear reactions, mass changes may be measurable

22 Chapter 422 Binding Energy Holds protons and neutrons together in the nucleus The higher the binding energy, the more stable the element

23 Chapter 423 Nuclear Fission Splitting the atom Break a large nucleus into smaller nuclei

24 Chapter 424 Nuclear Chain Reaction Neutrons from one fission event split further atoms Only certain isotopes, fissile isotopes, undergo nuclear chain reactions

25 Chapter 425 Manhattan Project How to sustain the nuclear reaction? How to enrich uranium to >90% 235 U? –Only 0.7% natural abundance How to make 239 Pu (another fissile isotope)? How to make a nuclear fission bomb?

26 Chapter 426 Radioactive Fallout Nuclear bomb detonated; radioactive materials may rain down miles away and days later –Some may be unreacted U or Pu –Radioactive isotopes produced during the explosion

27 Chapter 427 Nuclear Power Plants Provide ~20% U.S. electricity –France >70% Slow controlled release of energy Need 2.5–3.5% 235 U Problem with disposal of radioactive waste

28 Chapter 428 Nuclear Fusion Reaction takes smaller nuclei and builds larger ones –Also called thermonuclear reactions Releases tremendous amounts of energy –1 g of H would release same as 20 tons of coal

29 Chapter 429 End of Chapter 4

30 Chapter 430 Radioisotopes Radioactive decay – Many isotopes are unstable Radioisotopes –Nuclei that undergo radioactive decay –May produce one or more types of radiation

31 Chapter 431 Natural Radioactivity Background radiation –What occurs from natural sources –>80% of radioactivity exposure

32 Chapter 432 Nuclear Equations Elements may change in nuclear reactions Total mass and sum of atomic numbers must be the same MUST specify isotope

33 Chapter 433 Alpha Decay Nucleus loses particle –Mass decreases by 4 and atomic number decreases by 2

34 Chapter 434 Beta Decay Nucleus loses particle – No change in mass but atomic number increases

35 Chapter 435 Positron Emission Loses a positron –Equal mass but opposite charge of an electron –Decrease in atomic number and no change in mass – +

36 Chapter 436 Electron Capture Nucleus absorbs an electron and then releases an X-ray Mass number stays the same and atomic number decreases

37 Chapter 437 Gamma Radiation Release of high-energy photon – Typically occurs after another radioactive decay No change in mass number or atomic number

38 Chapter 438 Artificial Transmutation Transmutation changes one element into another –Middle Ages: change lead to gold In 1919 Rutherford established protons as fundamental particles –Basic building blocks of nuclei

39 Chapter 439 Example 4.1 Balancing Nuclear Equations Write balanced nuclear equations for each of the following processes. In each case, indicate what new element is formed. a. Plutonium-239 emits an alpha particle when it decays. b. Protactinium-234 undergoes beta decay. c. Carbon-11 emits a positron when it decays. d. Carbon-11 undergoes electron capture. Solution a. We start by writing the symbol for plutonium-239 and a partial equation showing that one of the products is an alpha particle (helium nucleus): Pu 4242 He + ? Mass and charge are conserved. The new element must have a mass of 239 – 4 = 235 and a charge of 94 – 2 = 92. The nuclear charge (atomic number) of 92 identifies the element as uranium (U): Pu 4242 He U

40 Chapter 440 Example 4.1 Balancing Nuclear Equations (cont.) b. Write the symbol for protactinium-234 and a partial equation showing that one of the products is a beta particle (electron): Pa 0–10–1 e + ? The new element still has a mass number of 234. It must have a nuclear charge of 92 in order for the total charge to be the same on each side of the equation. The nuclear charge identifies the new atom as another isotope of uranium (U): Pr 0–10–1 e U c. Write the symbol for carbon-11 and a partial equation showing that one of the products is a positron: 11 6 C e + ? To balance the equation, a particle with a mass number of 11 and an atomic number of 5 (B) is required: 11 6 C e B

41 Chapter 441 As mentioned in the text, positron emission and electron capture result in identical changes in atomic number, and therefore the identical elements are formed! Also, as parts (c) and (d) illustrate, C-11 (and certain other nuclei) can undergo several different types of radioactive decay processes. Example 4.1 Balancing Nuclear Equations (cont.) Write balanced nuclear equations for each of the following processes. In each case, indicate what new element is formed. Exercise 4.1 a. Radium-226 decays by alpha emission. b. Sodium-24 undergoes beta decay. c. Gold-188 decays by positron emission. d. Argon-37 undergoes electron capture C 0–10–1 e d. We write the symbol for carbon-11 and a partial equation showing it capturing an electron: + ? 11 6 C 0–10–1 e 11 5 B To balance the equation, the product must have a mass number of 11 and an atomic number of 5 (B): +

42 Chapter 442 Example 4.5 When potassium-39 is bombarded with neutrons, chlorine-36 is produced. What other particle is emitted? Cl + ? n K + Solution Write a balanced nuclear equation. To balance the equation, we need four mass units and two charge units (that is, a particle with a nucleon number of 4 and an atomic number of 2). Thats an alpha particle. Cl n K + He 4242 Technetium-97 is produced by bombarding molybdenum-96 with a deuteron (hydrogen-2 nucleus). What other particle is emitted? Exercise 4.5 Tc + ? H Mo +

43 Chapter 443 Example 4.6 One of the isotopes used for PET scans is oxygen-15, a positron emitter. What new element is formed when oxygen-15 decays? Phosphorus-30 is a positron-emitting radioisotope suitable for use in PET scans. What new element is formed when phosphorus-30 decays? Exercise 4.6 Solution First write the nuclear equation e + ? 15 8 O The nucleon number does not change, but the atomic number becomes 8 – 1, or 7; and so the new product is nitrogen-15: e O 15 7 N

44 Chapter 444

45 Chapter 445

46 Chapter 446

47 Chapter 447

48 Chapter 448

49 Chapter 449

50 Chapter 450

51 Chapter 451

52 Chapter 452

53 Chapter 453

54 Chapter 454

55 Chapter 455

56 Chapter 456

57 Chapter 457

58 Chapter 458


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