1. 1 Material was developed by combining Janusa’s material with the lecture outline provided with Ebbing, D. D.; Gammon, S. D. General Chemistry, 8th ed., Houghton Mifflin, New York, NY, 2005. Majority of figures/tables are from the Ebbing lecture outline. Section 20 Nuclear Chemistry

2. 2 Material was developed by combining Janusa’s material with the lecture outline provided with Ebbing, D. D.; Gammon, S. D. General Chemistry, 8th ed., Houghton Mifflin, New York, NY, 2005. Majority of figures/tables are from the Ebbing lecture outline. Nuclear Chemistry Radioactive decay is the process in which a nucleus spontaneously disintegrates, giving off radiation. Radiation are the particles or rays emitted. Radiation comes from the nucleus as a result of an alteration in nuclear composition or structure. This occurs in a nucleus that is unstable and hence radioactive. Nuclear symbols are used to designate the nucleus and consists of - Atomic symbol (element symbol) - Atomic number (Z - #protons) - Mass number (A - #protons + #neutrons)

3. 3 Material was developed by combining Janusa’s material with the lecture outline provided with Ebbing, D. D.; Gammon, S. D. General Chemistry, 8th ed., Houghton Mifflin, New York, NY, 2005. Majority of figures/tables are from the Ebbing lecture outline. atomic symbol atomic number number of protons mass number number of protons and neutrons This symbol is the same as writing boron-11 and defines an isotope of boron. In nuclear chemistry this is often called a nuclide. This is not the only isotope (nuclide) of boron.

4. 4 Material was developed by combining Janusa’s material with the lecture outline provided with Ebbing, D. D.; Gammon, S. D. General Chemistry, 8th ed., Houghton Mifflin, New York, NY, 2005. Majority of figures/tables are from the Ebbing lecture outline. Some isotopes are stable The unstable isotopes are the ones that produce radioactivity (emit particles); the actual process of radioactive decay. Radioactive decay is the process in which nucleus spontaneously disintegrates, giving off radiation.

5. 5 Material was developed by combining Janusa’s material with the lecture outline provided with Ebbing, D. D.; Gammon, S. D. General Chemistry, 8th ed., Houghton Mifflin, New York, NY, 2005. Majority of figures/tables are from the Ebbing lecture outline. Radioactivity Radioactivity was discovered by Antoine Henri Becquerel in 1896. –His work with uranium salts lead to the conclusion that the minerals gave off some sort of radiation. –This radiation was later shown to be separable by electric (and magnetic) fields into three types; alpha (  ), beta (  ), and gamma (  ) rays.

6. 6 Material was developed by combining Janusa’s material with the lecture outline provided with Ebbing, D. D.; Gammon, S. D. General Chemistry, 8th ed., Houghton Mifflin, New York, NY, 2005. Majority of figures/tables are from the Ebbing lecture outline. Radioactivity –Alpha rays (  ) bend away from a positive plate indicating they are positively charged. –They are known to consist of helium-4 nuclei (nuclei with two protons and two neutrons). –Slow moving (relatively large mass compared to other nuclear particles; therefore, moves slow - 10% speed of light) –Stopped by small barriers as thin as few pages of paper. –Symbolized in the following ways:

7. 7 Material was developed by combining Janusa’s material with the lecture outline provided with Ebbing, D. D.; Gammon, S. D. General Chemistry, 8th ed., Houghton Mifflin, New York, NY, 2005. Majority of figures/tables are from the Ebbing lecture outline. Radioactivity –Beta rays (  ) bend in the opposite direction indicating they have a negative charge. They are known to consist of high speed electrons (90% speed of light). Emitted from the nucleus by conversion of neutron into a proton. Higher speed particles; therefore, more penetrating than alpha particles (stopped by only more dense materials such as wood, metal, or several layers of clothing). The symbol is basically equivalent to electron

8. 8 Material was developed by combining Janusa’s material with the lecture outline provided with Ebbing, D. D.; Gammon, S. D. General Chemistry, 8th ed., Houghton Mifflin, New York, NY, 2005. Majority of figures/tables are from the Ebbing lecture outline. Radioactivity –Gamma rays (  ) are unaffected by electric and magnetic fields. –They have been shown to be a form of electromagnetic radiation (pure energy) similar to x rays, but higher in energy and shorter in wavelength. –Alpha and beta radiation are matter; contains p, n, or e while gamma is pure energy (no p, n, e). –Highly energetic, the most penetrating form of radiation (barriers of lead, concrete, or more often, a combination is required for protection. –Symbol is

9. 9 Material was developed by combining Janusa’s material with the lecture outline provided with Ebbing, D. D.; Gammon, S. D. General Chemistry, 8th ed., Houghton Mifflin, New York, NY, 2005. Majority of figures/tables are from the Ebbing lecture outline. Nuclear Equations A nuclear equation is a symbolic representation of a nuclear reaction using nuclide symbols. –For example, the nuclide symbol for uranium-238 is

10. 10 Material was developed by combining Janusa’s material with the lecture outline provided with Ebbing, D. D.; Gammon, S. D. General Chemistry, 8th ed., Houghton Mifflin, New York, NY, 2005. Majority of figures/tables are from the Ebbing lecture outline. Nuclear Equations –The radioactive decay of by alpha-particle emission (loss of a nucleus) is written –Reactant and product nuclei are represented in nuclear equations by their nuclide symbol.

11. 11 Material was developed by combining Janusa’s material with the lecture outline provided with Ebbing, D. D.; Gammon, S. D. General Chemistry, 8th ed., Houghton Mifflin, New York, NY, 2005. Majority of figures/tables are from the Ebbing lecture outline. Nuclear Equations –Other particles are given the following symbols. Neutron Gamma photon Protonor Electron or Positronor

12. 12 Material was developed by combining Janusa’s material with the lecture outline provided with Ebbing, D. D.; Gammon, S. D. General Chemistry, 8th ed., Houghton Mifflin, New York, NY, 2005. Majority of figures/tables are from the Ebbing lecture outline. Nuclear Equations In a nuclear equation, you do not balance the elements, instead... –the total mass on each side of the reaction arrow must be identical (this means that the sum of the superscripts for the products must equal the sum of the superscripts for the reactants). –the sum of the atomic numbers on each side of the reaction arrow must be identical (this means that the sum of the subscripts for the products must equal the sum of the subscripts for the reactants).

13. 13 Material was developed by combining Janusa’s material with the lecture outline provided with Ebbing, D. D.; Gammon, S. D. General Chemistry, 8th ed., Houghton Mifflin, New York, NY, 2005. Majority of figures/tables are from the Ebbing lecture outline. Alpha Decay 238 = 234 + 4 92 = 90 + 2 mass number atomic number Ex. Plutonium 239 emits an alpha particle when it decays, write the balanced nuclear equation.

14. 14 Material was developed by combining Janusa’s material with the lecture outline provided with Ebbing, D. D.; Gammon, S. D. General Chemistry, 8th ed., Houghton Mifflin, New York, NY, 2005. Majority of figures/tables are from the Ebbing lecture outline. Beta Decay Ex. Protactinium 234 undergoes beta decay. Write the balanced nuclear equation.

15. 15 Material was developed by combining Janusa’s material with the lecture outline provided with Ebbing, D. D.; Gammon, S. D. General Chemistry, 8th ed., Houghton Mifflin, New York, NY, 2005. Majority of figures/tables are from the Ebbing lecture outline. A Problem To Consider Technetium-99 is a long-lived radioactive isotope of technetium. Each nucleus decays by emitting one beta particle. What is the product nucleus? –The nuclear equation is –From the superscripts, you can write

16. 16 Material was developed by combining Janusa’s material with the lecture outline provided with Ebbing, D. D.; Gammon, S. D. General Chemistry, 8th ed., Houghton Mifflin, New York, NY, 2005. Majority of figures/tables are from the Ebbing lecture outline. A Problem To Consider Technetium-99 is a long-lived radioactive isotope of technetium. Each nucleus decays by emitting one beta particle. What is the product nucleus? –The nuclear equation is –Similarly, from the subscripts, you get

17. 17 Material was developed by combining Janusa’s material with the lecture outline provided with Ebbing, D. D.; Gammon, S. D. General Chemistry, 8th ed., Houghton Mifflin, New York, NY, 2005. Majority of figures/tables are from the Ebbing lecture outline. A Problem To Consider Technetium-99 is a long-lived radioactive isotope of technetium. Each nucleus decays by emitting one beta particle. What is the product nucleus? –The nuclear equation is –Hence A = 99 and Z = 44 (Ruthenium), so the product is

18. 18 Material was developed by combining Janusa’s material with the lecture outline provided with Ebbing, D. D.; Gammon, S. D. General Chemistry, 8th ed., Houghton Mifflin, New York, NY, 2005. Majority of figures/tables are from the Ebbing lecture outline. Nuclear Structure and Stability Binding Energy - the energy that holds the protons, neutrons, and other particles together in the nucleus. Binding energy is very large for unstable isotopes. When isotopes decay (forming more stable isotopes,) binding energy is released (go to lower E state; more stable arrangement.

19. 19 Material was developed by combining Janusa’s material with the lecture outline provided with Ebbing, D. D.; Gammon, S. D. General Chemistry, 8th ed., Houghton Mifflin, New York, NY, 2005. Majority of figures/tables are from the Ebbing lecture outline. Important factors for stable isotopes; nuclear stability correlates with: –Ratio of neutrons to protons in the isotope. –Nuclei with large number of protons (84 or more) tend to be unstable. –The “magic numbers” of 2, 8, 20, 50, 82, or 126 help determine stability. These numbers of protons or neutrons are stable. These numbers, called magic numbers, are the numbers of nuclear particles in a completed shell of protons or neutrons. –Even numbers of protons or neutrons are generally more stable than those with odd numbers. –All isotopes (except 1 H) with more protons than neutrons are unstable.

20. 20 Material was developed by combining Janusa’s material with the lecture outline provided with Ebbing, D. D.; Gammon, S. D. General Chemistry, 8th ed., Houghton Mifflin, New York, NY, 2005. Majority of figures/tables are from the Ebbing lecture outline. Nuclear Stability Several factors appear to contribute the stability of a nucleus. –when you plot each stable nuclide on a graph of neutrons vs. protons, these stable nuclei fall in a certain region, or band. –The band of stability is the region in which stable nuclides lie in a plot of number of neutrons against number of protons.

21. 21 Material was developed by combining Janusa’s material with the lecture outline provided with Ebbing, D. D.; Gammon, S. D. General Chemistry, 8th ed., Houghton Mifflin, New York, NY, 2005. Majority of figures/tables are from the Ebbing lecture outline. Figure : Band of stability.

22. 22 Material was developed by combining Janusa’s material with the lecture outline provided with Ebbing, D. D.; Gammon, S. D. General Chemistry, 8th ed., Houghton Mifflin, New York, NY, 2005. Majority of figures/tables are from the Ebbing lecture outline. Predicting the Type of Radioactive Decay Nuclides outside the band of stability are generally radioactive. –Nuclides to the left of the band have more neutrons than that needed for a stable nucleus. –These nuclides tend to decay by beta emission because it reduces the neutron-to-proton ratio.

23. 23 Material was developed by combining Janusa’s material with the lecture outline provided with Ebbing, D. D.; Gammon, S. D. General Chemistry, 8th ed., Houghton Mifflin, New York, NY, 2005. Majority of figures/tables are from the Ebbing lecture outline. Predicting the Type of Radioactive Decay Nuclides outside the band of stability are generally radioactive. –In contrast, nuclides to the right of the band of stability have a neutron-to-proton ratio smaller than that needed for a stable nucleus. –These nuclides tend to decay by positron emission or electron capture because it increases the neutron to proton ratio.

24. 24 Material was developed by combining Janusa’s material with the lecture outline provided with Ebbing, D. D.; Gammon, S. D. General Chemistry, 8th ed., Houghton Mifflin, New York, NY, 2005. Majority of figures/tables are from the Ebbing lecture outline. Predicting the Type of Radioactive Decay Nuclides outside the band of stability are generally radioactive. –In the very heavy elements, especially those with Z greater than 83, radioactive decay is often by alpha emission.

25. 25 Material was developed by combining Janusa’s material with the lecture outline provided with Ebbing, D. D.; Gammon, S. D. General Chemistry, 8th ed., Houghton Mifflin, New York, NY, 2005. Majority of figures/tables are from the Ebbing lecture outline.

26. 26 Material was developed by combining Janusa’s material with the lecture outline provided with Ebbing, D. D.; Gammon, S. D. General Chemistry, 8th ed., Houghton Mifflin, New York, NY, 2005. Majority of figures/tables are from the Ebbing lecture outline. Types of Radioactive Decay There are six common types of radioactive decay. –Alpha emission (abbreviated  ): emission of a nucleus, or alpha particle, from an unstable nucleus. –An example is the radioactive decay of radium-226.

27. 27 Material was developed by combining Janusa’s material with the lecture outline provided with Ebbing, D. D.; Gammon, S. D. General Chemistry, 8th ed., Houghton Mifflin, New York, NY, 2005. Majority of figures/tables are from the Ebbing lecture outline. Types of Radioactive Decay There are six common types of radioactive decay. –Beta emission (abbreviated  or  - ): emission of a high speed electron from a unstable nucleus. –This is equivalent to the conversion of a neutron to a proton. –An example is the radioactive decay of carbon-14.

28. 28 Material was developed by combining Janusa’s material with the lecture outline provided with Ebbing, D. D.; Gammon, S. D. General Chemistry, 8th ed., Houghton Mifflin, New York, NY, 2005. Majority of figures/tables are from the Ebbing lecture outline. Types of Radioactive Decay There are six common types of radioactive decay. –Positron emission (abbreviated  + ): emission of a positron from an unstable nucleus. –This is equivalent to the conversion of a proton to a neutron. –The radioactive decay of techencium-95 is an example of positron emission.

29. 29 Material was developed by combining Janusa’s material with the lecture outline provided with Ebbing, D. D.; Gammon, S. D. General Chemistry, 8th ed., Houghton Mifflin, New York, NY, 2005. Majority of figures/tables are from the Ebbing lecture outline. Types of Radioactive Decay There are six common types of radioactive decay. –Electron capture (abbreviated EC): the decay of an unstable nucleus by capturing, or picking up, an electron from an inner orbital of an atom. –In effect, a proton is changed to a neutron, as in positron emission. –An example is the radioactive decay of potassium-40.

30. 30 Material was developed by combining Janusa’s material with the lecture outline provided with Ebbing, D. D.; Gammon, S. D. General Chemistry, 8th ed., Houghton Mifflin, New York, NY, 2005. Majority of figures/tables are from the Ebbing lecture outline. Types of Radioactive Decay There are six common types of radioactive decay. –Gamma emission (abbreviated  ): emission from an excited nucleus of a gamma photon, corresponding to radiation with a wavelength of about 10 -12 m. –In many cases, radioactive decay produces a product nuclide in a metastable excited state. –The excited state is unstable and emits a gamma photon and goes to a lower energy state (more stable). The atomic mass and number do not change. –An example is metastable technetium-99.

31. 31 Material was developed by combining Janusa’s material with the lecture outline provided with Ebbing, D. D.; Gammon, S. D. General Chemistry, 8th ed., Houghton Mifflin, New York, NY, 2005. Majority of figures/tables are from the Ebbing lecture outline. Types of Radioactive Decay There are six common types of radioactive decay. –Spontaneous fission: the spontaneous decay of an unstable nucleus in which a heavy nucleus of mass number greater than 89 splits into lighter nuclei and energy is released. –For example, uranium-236 undergoes spontaneous fission.

32. 32 Material was developed by combining Janusa’s material with the lecture outline provided with Ebbing, D. D.; Gammon, S. D. General Chemistry, 8th ed., Houghton Mifflin, New York, NY, 2005. Majority of figures/tables are from the Ebbing lecture outline. Rate of Radioactive Decay The rate of radioactive decay, that is the number of disintegrations per unit time, is proportional to the number of radioactive nuclei in the sample. –You can express this rate mathematically as where N t is the number of radioactive nuclei at time t, and k is the radioactive decay constant.

33. 33 Material was developed by combining Janusa’s material with the lecture outline provided with Ebbing, D. D.; Gammon, S. D. General Chemistry, 8th ed., Houghton Mifflin, New York, NY, 2005. Majority of figures/tables are from the Ebbing lecture outline. Rate of Radioactive Decay –All radioactive decay follows first order kinetics as outlined in kinetics chapter. –Therefore, the half-life of a radioactive sample is related only to the radioactive decay constant. –The half-life, t½,of a radioactive nucleus is the time required for one-half of the nuclei in a sample to decay. –The first-order relationship between t ½ and the decay constant k is

34. 34 Material was developed by combining Janusa’s material with the lecture outline provided with Ebbing, D. D.; Gammon, S. D. General Chemistry, 8th ed., Houghton Mifflin, New York, NY, 2005. Majority of figures/tables are from the Ebbing lecture outline. Rate of Radioactive Decay Once you know the decay constant, you can calculate the fraction of radioactive nuclei remaining (N t/ N o ) after a given period of time. –Recall the first-order time-concentration equation is –Or if we don’t know k we can substitute k = 0.693/t ½ and get

35. 35 Material was developed by combining Janusa’s material with the lecture outline provided with Ebbing, D. D.; Gammon, S. D. General Chemistry, 8th ed., Houghton Mifflin, New York, NY, 2005. Majority of figures/tables are from the Ebbing lecture outline. A Problem To Consider Phosphorus-32 has a half-life of 14.3 days. What fraction of a sample of phosphorus-32 would remain after 5.5 days? HW 51

36. 36 Material was developed by combining Janusa’s material with the lecture outline provided with Ebbing, D. D.; Gammon, S. D. General Chemistry, 8th ed., Houghton Mifflin, New York, NY, 2005. Majority of figures/tables are from the Ebbing lecture outline. Nuclear Fission and Nuclear Fusion Nuclear fission is a nuclear reaction in which a heavy nucleus splits into lighter nuclei and energy is released. –For example, one of the possible mechanisms for the decay of californium-252 is

37. 37 Material was developed by combining Janusa’s material with the lecture outline provided with Ebbing, D. D.; Gammon, S. D. General Chemistry, 8th ed., Houghton Mifflin, New York, NY, 2005. Majority of figures/tables are from the Ebbing lecture outline. Nuclear Fission and Nuclear Fusion –In some cases a nucleus can be induced to undergo fission by bombardment with neutrons. –When uranium-235 undergoes fission, more neutrons are released creating the possibility of a chain reaction. –A chain reaction is a self-sustaining series of nuclear fissions caused by the absorption of neutrons released from previous nuclear fissions.

38. 38 Material was developed by combining Janusa’s material with the lecture outline provided with Ebbing, D. D.; Gammon, S. D. General Chemistry, 8th ed., Houghton Mifflin, New York, NY, 2005. Majority of figures/tables are from the Ebbing lecture outline. Chain reaction - the reaction sustains itself by producing more neutrons

39. 39 Material was developed by combining Janusa’s material with the lecture outline provided with Ebbing, D. D.; Gammon, S. D. General Chemistry, 8th ed., Houghton Mifflin, New York, NY, 2005. Majority of figures/tables are from the Ebbing lecture outline. Nuclear Fission and Nuclear Fusion Nuclear fusion is a nuclear reaction in which light nuclei combine to give a stable heavy nucleus plus possibly several neutrons, and energy is released. –Such fusion reactions have been observed in the laboratory using particle accelerators. –Sustainable fusion reactions require temperatures of about 100 million o C.

40. 40 Material was developed by combining Janusa’s material with the lecture outline provided with Ebbing, D. D.; Gammon, S. D. General Chemistry, 8th ed., Houghton Mifflin, New York, NY, 2005. Majority of figures/tables are from the Ebbing lecture outline. Nuclear Fission and Nuclear Fusion Nuclear fusion is a nuclear reaction in which a light nuclei combine to give a stable heavy nucleus plus possibly several neutrons, and energy is released. Fusion (to join together) - combination of two small nuclei to form a larger nucleus. Large amounts of energy is released. Best example is the sun. An Example: