1. Nuclear Chemistry

2. Chemical Reactivity “Normal” Chemical Behavior Example: 2H 2 + O 2  2H 2 O “Atoms that go in must come out.” Nuclei of atoms remain the same. Nuclear Chemistry Resembles Alchemy “Turning Lead into Gold!” Nucleus changes as reactions occur Radioactivity

3. Nuclear Stability Most stable nuclei have a 1:1 neutron: proton ratio As number of protons increase, stability decreases All isotopes with an atomic number > 83 are radioactive. Elements below 83 may have some isotopes that are radioactive, but not all of them will be. Ex: 14 C Half-life gives an indication of stability of nucleus – see Table N.

4. Band of Stability

5. Radioactivity Radioactive elements decay spontaneously. Nothing will stop the decay. Decay = Transmutation change of one element into another change in atomic number Not necessarily bad!

6. Decay Series

7. Transmutation equations 238 U 92  4 He 2 + 234 Th 90 Each element symbol has 2 numbers. Top number = mass of particle Bottom number = charge of particle. Mass and charge are conserved. 37 Ca 20  0 e +1 + 37 K 19

8. Decay Modes Natural decay vs. Artificial Decay Natural Decay Alpha decay -  Beta decay -  - Gamma decay -  Positron Emission -  + Reference Table ‘O’ Reference Table ‘N’ Artifical Decay = Nuclear Bombardment Particle accelerator

9. Alpha decay Alpha particle nucleus of He atom : 4 He 2 or 4  2 +2 charge – symbol on Ref. Table “O” Attracted to negative charges Slow moving – travels only approx. 6 in. Stopped by piece of paper Alpha Transmutation natural atomic number decreases by 2 mass number deceases by 4 Ex. 238 U 92  4 He 2 + 234 Th 90

10. Plutonium  Uranium 240 Pu 94  236 U 92 + 4 He 2

11. Beta Decay Beta Particle Beta = an electron = 0 e -1 -1 charge, 0 mass attracted to positive charges WHAT? An electron in the nucleus??? Produced by “decomposition” of neutron into a proton and an electron: 1 n 0  1 p 1 + 0 e -1 Faster moving than alpha (smaller), travels farther, stopped by Al foil or thick cardboard Beta Transmutation natural atomic number increases by 1 mass number remains the same Ex. 239 U 92  0 e -1 + 239 Np 93

12. Cesium  Barium 137 Cs 55  137 Ba 56 + 0 e -1

13. Gamma Rays Energy only no mass, charge, volume like X-ray energy except more powerful – attracted to nothing Travels though thick material can be stopped by thick metal, Pb, concrete Travels at speed of light Symbol – Ref. Table “O”

14. Gamma Decay No change to nucleus

15. Positron Emission Rare A proton decays into a neutron and a positron: 1 p 1  1 n 0 + 0 e +1 Nucleus gives off a particle same size and mass as an electron but positive in charge. Example: 37 Ca 20  0 e +1 + 37 K 19

16. Sodium  Neon 22 Na 11  22 Ne 10 + 0 e +1

17. Half-Life Length of time it takes for one half of a sample of any radioisotope to undergo transmutation Reference Table “N” indicates both the half-life and decay mode Nothing affects the half-life of an element each radioisotope has its own half-life Can be used as an indication of stability

18. Nuclear Fission In a fission reaction, an atom absorbs a neutron and splits into two or more smaller atoms and energy 235 U 92 + 1 n 0  141 Ba 56 + 92 Kr 36 + 3 1 n 0 + energy The reaction is an uncontrolled chain reaction if it occurs as an atomic bomb The energy produced can be explained using Einstein’s equation: E=mc 2 (next slide) Other elements capable of fission include 239 Pu and 233 U.

19. Mass Defect The amount by which the mass of an atomic nucleus is less than the sum of the masses of its constituent particles. Accounted for by E=mc 2 And Nuclear Binding Energy

20. Nuclear Power Controlled fission Reaction = energy Energy boils water Steam turns turbine Turbine turns generator Generator produces electrical E.

21. Other details… Plant Operation: Fuel U 235 or Pu 239 Moderator – slows neutrons water, heavy water, graphite Control rods – absorb neutrons boron &/or cadmium) used to stop or start reaction Coolant – control temperature water, heavy water, liquid sodium Shielding – contain radiation reinforced concrete, steel, water

22. Nuclear Power Benefits: large quantities of energy from small masses; no air pollution; low operation cost Negatives: residual radioactive waste; high initial cost; potential thermal pollution; release of radiation from accidents (ex. Chernobyl, Three Mile Island, Japan)

23. Fusion Two nuclei unite under tremendous heat and pressure forms a heavier nucleus the difference in attraction needed for new atom is released as energy 2 H 1 + 2 H 1  4 He 2 + energy More powerful than fission Ex.- the sun, hydrogen bomb Uncontrollable with present technology Ultimate source of energy

24. Uses of Radioisotopes Tracers – ex: C-14 follow chemical or biological reactions Medical – ex: Tc-99, I-131, Ra, Co-60 detection/treatment of diseases Food storage – destroy bacteria, yeast, mold permits storage w/o refrigeration for longer periods Radioactive dating - U-238 to Pb-206, C-14 Industrial