Nuclear Chemistry

1. Nuclear Chemistry Unstable Nuclei and Radioactive Decay

3. Radioactivity • Chemical reaction involves only an atom’s electrons – the nucleus remains unchanged • Nuclear reactioninvolves a change in an atom’s nucleus (p+ or n0 number) • Radioactivity is when substances spontaneously emit radiation • The rays and particles emitted are radiation

4. Radioactivity • Radioactive atoms emit radiation because their nuclei are unstable (gain stability by losing energy) • Radioactive decay is when atoms lose energy by emitting radiation in a spontaneous process. Atoms keep decaying until they form stable, nonradioactive atoms.

5. Types of Radiation • Alpha, beta, and gamma radiation have different amounts of electrical charge and are affected differently by an electric field • Radioactive source, two plates (+,-), stream of alpha, beta, and gamma rays

6. Alpha Radiation • 2p+ and 2n0 • Particles deflected to (-) plate • Extra protons form new element • Nuclear equation: • 22688Ra → 22286Rn + 42He radium-226radon-222alpha particle

8. Beta Radiation • Fast moving e- • -1 charge • Particles deflected to (+) plate • Nuclear equation: • 146C → 147N + 0-1β carbon-14 nitrogen-14 beta particle

10. Gamma Radiation • High energy radiation without mass or electrical charge • Particles are not deflected by electric or magnetic fields • Unable to form a new atom by themselves since they are mass-less • They accompany other types of radiation in reactions • 23892U →23490Th + 42He + 200γ Uranium-238 thorium-234 alpha particle gamma rays

12. Characteristics of Radiation

13. Penetrating Power

14. Human Body

15. Nuclear Stability • Elements > atomic number 83 are naturally radioactive • Ratio of p+ to n0 determines the stability of an atom • Atoms with too many or too few neutrons are unstable • Ratio of 1.5 : 1

16. Fusion Reactions • Nuclear process in which two light nuclei combine to form a single heavier nucleus. Examples: thermonuclear weapons and in future nuclear reactors

17. Fusion Reactions • The sum of the masses of the product nuclei is less than the sum of the masses of the initial fusing nuclei. • E=mc2, explains that the mass that is lost it converted into energy carried away by the fusion products.

18. Fusion and our Universe • Hydrogen isotopes collide in a star and fuse forming a helium nucleus • Lighter elements fuse and form heavier elements. These reactions continue until the nuclei reach iron, the nucleus with the most binding energy. No more fusion occurs in a star because it is energetically unfavorable to produce higher masses. Once a star has converted a large fraction of its core's mass to iron, it has almost reached the end of its life.

19. Fission Reactions    Fission is a nuclear process in which a heavy nucleus splits into two smaller nuclei. An example of a fission reaction that was used in the first atomic bomb and is still used in nuclear reactors is: 235U + n ----> 134Xe + 100Sr + 2n

20. FissionReactions • Fission reactions can produce any combination of lighter nuclei so long as the number of protons and neutrons in the products sum up to those in the initial fissioning nucleus. As with fusion, a great amount of energy can be released in fission because for heavy nuclei, the summed masses of the lighter product nuclei is less than the mass of the fissioning nucleus

21. Fission • Fission is a process that has been occurring in the universe for billions of years. We have not only used fission to produce energy for nuclear bombs, but we also use fission peacefully everyday to produce energy in nuclear power plants

22. Fission • Nuclear energy is the most certain future fuel source that we have. Currently in the U.S. 107 nuclear reactors are producing about 17% of our energy requirements. The U.S. Currently has plans of building 42 more nuclear power plants in the next 20 years.

23. Downfalls to using Fission and Fusion as fuel sources… • Radioactive and toxic wastes • Fear/anxiety of terrorist bombing • Safe storage of toxic wastes? • Construction costs more than the energy it provides • Coal still used and causing environmental issues • Can cause health problems in humans

24. Practical Applications of Nuclear Power • Cheap • Efficient • Lower air pollution • Lower the price of electricity • Uranium is abundant on earth

25. Half Life • The time it takes for one-half of a radioisotope’s nuclei to decay into its products • The half-life of strontium-90 is 29 years

26. Half Life Amount remaining = (initial amount)(1/2)n n = the number of half-lives that have passed

27. Radioactive Decay Practice Practice Problem #1: If Gallium-68 has a half-live of 68.3 minutes, how much of a 10.0 mg sample is left after one half-life? Two half-lives? Three half-lives?

28. Radioactive Decay Practice Practice Problem #2: If the passing of five half-lives leaves 25.0 mg of a strontium-90 sample, how much was present in the beginning?