1. Lecture 364/28/06 Clean-up Day Sunday, April 30th at 11Am Hagan Lawn Sign up at the reach out center today Check in with Dan Socha on Sunday

2. Quiz 1. Consider the melting of ice. What are the signs (+ or -) for ΔH, ΔS, and ΔG for this process at -10º? 2. Describe an alpha particle? -10 ºC ΔH ΔS ΔG

3. Radioactive emissions positron (β + ) electron proton  positron (β) + neutron

4. Radioactive Electron capture Electron + proton  neutron

5. Examples

6. Belt of stability Belt of stability ends at element 83 Type of decay nuclei above belt of stability (high N/Z) nuclei below the belt of stability (low N/Z) nuclei with atomic # ≥ 84

7. Stability of Nuclei Out of > 300 stable isotopes: Even Odd Odd Even Z N 15752 505

8. Rates of radioactive decay Decay is not affected by temperature, pressure, or state of chemical combination

10. If you start with 1.5 mg of tritium 3 H, how much is left after 49.2 years? t 1/2 =12.3 years

12. Carbon dating in atmosphere t 1/2 =5730 years Ratio of 14 C/ 12 C constant until death, then 14 C/ 12 C decreases At death, 14 C has about 14 disintegrations per minute/gram (dpm/g)

13. Carbon-14 limitations 1. assume 14 C in atmosphere is constant 2. can’t date object < 100 years old 3. accuracy only ± 100 years 4. only good back to ~ 40, 000 years