1. Outline:4/16/07 Today: Chapter 22 (cont’d) Nuclear Chemistry - Modes of decay - Half-life calculations è Pick up leftover CAPA outside… è Special seminar Wednesday pm è Turn in Seminar reports – to me

2. Quiz #9 n Please put away books & papers. n Turn your paper over when done.

3. Quiz #9 n Please pass your quiz to the right…

4. Nuclear Reactions: n n Types of radioactive decay:   Alpha (  ), Beta (  ), and Gamma (  ) fission, fusion,  positron (   ), e  capture (EC)…. n Natural vs. induced reactions: Worksheet #13 Balancing equations

5. Worksheet #13 Remember: both top and bottom must balance on both sides of the equation (conservation of mass and charge!) Remember: both top and bottom must balance on both sides of the equation (conservation of mass and charge!) n Start filling in the blanks: nuclear equation writing

6. Worksheet #13 (a) 1 + 235 = 131 + ____ 0 + 92 = 53 + ____ 105 39 105 39 Y (b) 0 + ____ = 14   1 + ____ = 6 14 7 14 7 N (c) 60 = 0 + ____  27 =  1 + ____ 60 28 60 28 Ni

7. Radioactive Decay: 1st order First order decay : N = N 0 e  k t n Half-life:  ln(N/N 0 ) =  k t  ln(1/2) =  k t 1/2 0.693 = k t 1/2 t 1/2 : a convenient way to refer to k e.g. 14 C has k = 1.209 × 10  4 yr  1 ; what is its half-life?

8. 0.693 = k t 1/2  k = 1.209 × 10  4 yr  1 e.g. : If 10.0 g of Kennewick Man bone has 34.6 dpm of 14 C, and a present-day 10.0 g bone has 103.7 dpm, how old is Kennewick Man? t 1/2 = 0.683/k = 5730 yr  N/N 0 = e  k t or ln(N/N 0 ) =  k t  ln(34.6/103.7) =  k t t = 9080 yrs

9. Decay calculations: Where have you seen these before? Chapter 15 (pp. 627-630) = Kinetics PRACTICE!

10. Worksheet #13 - Question 2 0.02% of 1000g = 0.2 g 14 C 0.2 g  1mol/14g = 0.143 mol 14 C N/N 0 = 7.65e20 / 8.60e21 = 0.0889  ln (0.0889) =  k t   2.42 =  1.209 × 10  4 yr  1 t = 8.60e21 atoms 14 C 0.143 mol 14 C  6.022e23 atoms/mol t = 20,000 yr