Nuclear reactions involve changes to atomic nuclei, whereas chemical reactions only involve rearrangement of electrons. Nuclear reactions can release large amounts of energy and produce new elements, while chemical reactions typically involve smaller energy changes and atoms remain the same elements. Radioactive decay is an example of a nuclear reaction where an unstable atomic nucleus spontaneously transforms into a more stable nucleus by emitting particles or electromagnetic radiation.

1. Nuclear Chemistry Ch 4.5 & 25

2. Nuclear Reactions vs. Normal Chemical Changes Nuclear reactions- reactions that take place inside the nucleus of an atom CHEMICAL REACTIONS NUCLEAR REACTIONS Bonds are broken and formed Nuclei emit particles and/or rays Atoms remain unchanged, only rearranged 2H 2 + O 2  2H 2 O Atoms are changed into other atoms of different elements Involve valence electrons Involves the nucleus, P + , N 0 , e- Small energy changes large energy changes ( BINDING Energy) Rate influenced by conc, temp., pressure and catalyst Not affected by those

3. Radioactivity One of the pieces of evidence for the fact that atoms are made of smaller particles came from the work of Marie Curie a Polish scientist (1876-1934). She discovered radioactivity, the spontaneous disintegration of some elements into smaller pieces (other elements).

4. Radioactivity Many nuclei are radioactive. This means they are unstable and will decay by emitting a particle or ray, transforming the nucleus into another nucleus, or into a lower energy state. A chain of decays takes place until a stable nucleus is reached.

5. Radioactivity & Unstable Atoms If # of neutrons is too high or too low, the nucleus becomes unstable and emits energy. Any atom containing an unstable nucleus is called a radioactive isotope or radioisotope * **More than 1,500 different nuclei are known. Of those, only 264 are stable and do not decay or change with time. These nuclei are in a region called the band of stability.

6. Isotopes have the same number of p____, different number of n_____ Another way to show an isotope is to have the mass number follow the name of the element (Carbon- 14 or C- 14 )

7. Isotopes 39 19 K ; 40 19 K 14 6 C ; 12 6 C Superscript is the mass number Subscript is the atomic number

8. Types of Nuclear Radiation Alpha 2.Beta 3. Gamma

9. Alpha Decay Alpha particle —a positively charged particle (helium isotope ) made up of two p+ & two n o the least penetrating can be stopped by a sheet of paper Symbols:  ,

10. Alpha Decay An alpha particle looks like a helium atom ( 4 2 He)  mass reduces by 4 ,the atomic # reduces by 2 Examples: 238 92 U  234 90 Th + 4 2 He 209 84 Po  205 82 Pb + 4 2 He Parent cell Daughter cell

11. Beta Decay A beta particle is an e- emitted by an unstable nucleus can be stopped by a thin sheet of metal such as aluminum Symbols:  ,

12. Beta Decay A beta particle is written 0 -1 e (  ) mass remains the same & the atomic # increases by one Examples: 214 82 Pb  214 83 Bi + 0 -1 e 218 84 Po  218 85 At + 0 -1 e

13. Gamma decay A gamma ray is a penetrating ray of energy (photon) emitted by an unstable nucleus Gamma rays are energy waves that travel through space at the speed of light Symbols:  ,

14. Gamma decay (  ) atomic # and mass remain the same, but the energy of nucleus decreases Gamma rays are often emitted along with alpha &/or beta particles Gamma rays can be stopped by several centimeters of lead or by several meters of concrete

15. Penetrating Ability

16. Other Nuclear Particles Neutron Positron – a positive electron Proton – usually referred to as hydrogen-1 Any other elemental isotope

17. Balancing Nuclear Reactions In the reactants (starting materials – on the left side of an equation) and products (final products – on the right side of an equation) Atomic numbers must balance and Mass numbers must balance Use a particle or isotope to fill in the missing protons and neutrons

18. Nuclear Reactions Reactions that occur naturally as nuclei strive to be stable.

19. Learning Check What radioactive isotope is produced in the following bombardment of boron? 10 B + 4 He ? + 1 n 5 2 0

20. Learning Check What radioactive isotope is produced in the following bombardment of boron? 10 B + 4 He 13 N + 1 n 5 2 7 0

21. Write Nuclear Equations! Write the nuclear equation for the beta emitter Co-60. 60 Co  60 Ni + 0 e 27 28 -1

22. Half-Life HALF-LIFE is the time that it takes for 1/2 a sample to decompose. The rate of a nuclear transformation depends only on the “reactant” concentration. Amount remaining = Initial amount x (1/2) t/T t/T, where t is the elapsed time and T is the duration of the half-life.

23. Half-Life Decay of 20.0 mg of 15 O. What remains after 3 half-lives? After 5 half-lives? 2.5mg 0.625mg

24. Kinetics of Radioactive Decay For each duration (half-life), one half of the substance decomposes. For example: Ra-234 has a half-life of 3.6 days If you start with 50 grams of Ra-234 After 3.6 days > 25 grams After 7.2 days > 12.5 grams After 10.8 days > 6.25 grams

25. Learning Check! The half life of I-123 is 13 hr. How much of a 64 mg sample of I-123 is left after 39 hours?

26. Detecting Radiation Devices used to detect radiation include Geiger counters & film badges

27. Radiocarbon Dating Radioactive C-14 is formed in the upper atmosphere by nuclear reactions initiated by neutrons in cosmic radiation 14 N + 1 o n ---> 14 C + 1 H The C-14 is oxidized to CO 2 , which circulates through the biosphere. When a plant dies, the C-14 is not replenished. But the C-14 continues to decay with t 1/2 = 5730 years. Activity of a sample can be used to date the sample.

28. Limits to Carbon Dating Some organic material must be present and must be from an organism that once lived. Cannot reliably detect objects more than 75,000 years old.

29. Radiation in Real life Radiation Everyday

30. Fission is the splitting of a nucleus into smaller fragments. Done by Neutron Bombardment Nuclear Fission

31. A uranium-235 nucleus is struck by a neutron with ordinary thermal energy. An unstable uranium-236 nucleus is formed, but it breaks into two fragments with the release of several neutrons. The neutrons can induce the fission of other uranium-235 nuclei. FISSION

33. Uranium-235 and Plutonium-239 are the only fissionable isotopes.

34. FISSION Since the one original neutron causing the reaction has resulted in the production of three neutrons , there is the possibility of a chain reaction occurring. A chain reaction

36. Atomic Bombs This is what happens in an atomic bomb. A fission bomb uses an uncontrolled nuclear fission chain reaction to release an enormous amount of energy in a small amount of time.

37. Nuclear Fission & POWER Currently about 103 nuclear power plants in the U.S. and about 435 worldwide. 17% of the world’s energy comes from nuclear.

38. Figure 25.11: Diagram of a nuclear power plant. A controlled fission chain reaction.

39. Fission Advantages: is the lack of air pollution. Disadvantages: include the risk of exposure & radioactive waste (takes hundreds of years to decay) Harris plant, near Raleigh Lake Harris

41. Nuclear Fusion Fusion small nuclei combine 2 H + 3 H 4 He + 1 n + 1 1 2 0 Occurs in the sun and other stars Energy

42. FUSION Fusion is the name given to the nuclear reaction whereby small nuclei are induced to join together into larger nuclei and release energy in the process. It is the reaction that "fuels" all stars including the Sun. A typical reaction that is taking place in the Sun is the fusion of two different isotopes of hydrogen to produce helium.

43. Nuclear Fusion 2 1 H + 2 1 H  4 2 He + energy Two small, positively-charged nuclei smash together at high temperatures and pressures to form one larger nucleus. A small bit of mass is destroyed and converted into a huge amount of energy, more than even fission.

44. Fusion We do not use fusion reactions for energy b/c of the extremely high temperatures needed to start the reaction & because the plasma would need to be contained.

45. FISSION AND FUSION Fission is the splitting of an atomic nucleus into two smaller parts Fusion is a process in which the nuclei of two atoms combine to form a larger nucleus

46. Nuclear Medicine: Imaging Thyroid imaging using Iodine-131 The radioisotope is used as a tracer. Must have a short half-life & can be eliminated from the body quickly.

47. Food Irradiation Food can be irradiated with  rays from 60 Co or 137 Cs. Irradiated milk has a shelf life of 3 mo. without refrigeration. USDA has approved irradiation of meats and eggs. “ Radura”  US FDA

48. Nuclear Music Nuclear Power to the People Natural Decay One Half Life to Live