1. Outline:4/13/07 Today: Start Chapter 22 Nuclear Chemistry - Definitions - Nuclear Stability - Modes of decay è CAPA 19 due tonight… è Special seminar Friday 4pm è Turn in Seminar reports – to me

2. Nuclear Chemistry: Some Definitions n n Nuclear chemistry…about nucleus n n Nucleus or nuclide ( a core made of protons and neutrons...called nucleons) n n Isotopes: Nuclides of the same element (i.e. with same number of protons) but with a different mass (i.e. a different number of neutrons.)

3. Remember Isotopes? n n Molar masses of elements = weighted averages of all isotopes A=mass number = protons + neutrons Z=atomic number= protons Molar mass 16 S 32.066 Periodic Table Nuclear Notation: X Z A S 16 32

4. Example: isotopic abundance n n Calculate the % abundances of 63 Cu and 65 Cu if the atomic weight is 63.546 amu and the exact masses of the isotopes are 62.93 and 64.93 amu respectively. (X)(62.93 amu) + (1  X)(64.93 amu) = 63.546 62.93X + 64.93  64.93X = 63.546 (62.93  64.93)X = 63.546  64.93  2X =  1.384 X = 0.692 & 1  X =.308 69.2% 63 Cu & 30.8 % 65 Cu

5. Nuclear Binding Energy If protons are positively charged, why does the nucleus stay together? If protons are positively charged, why does the nucleus stay together? Strong nuclear force: a force stronger than the Coulombic repulsion of the protons in the nucleusStrong nuclear force: a force stronger than the Coulombic repulsion of the protons in the nucleus The nucleus actually weighs less than the sum of its individual partsThe nucleus actually weighs less than the sum of its individual parts The difference in weight makes up the binding energy according to E=mc 2The difference in weight makes up the binding energy according to E=mc 2

8. Binding energy Large amount of energy, small mass (E=mc 2 ) Odd - Odd nuclei are unstable…. N  Z (light) ; N  1.5 × Z (heavy) Z max (so far)  118 Holds the nucleons together = strong Defines what makes a nucleus stable;

9. Valley of stability

11. So what happens to unstable nuclei? RadioactivityThey decay: Radioactivity transmutationOne nucleus turns into another: a process called “transmutation” Example: Alpha particle decay 241 Am  237 Np + 4 He 95 93 2 e.g. smoke detectors  particle Note that the reaction balances...

12. Historical: n n Types of radioactive decay:   Alpha (  ), Beta (  ), and Gamma (  ) fission, fusion,  positron (   ), e  capture (EC)…. DEMO: fiestaware, no-salt

13. Nuclear Chemistry Types of decays: Examples       EC fission fusion alpha beta (electron) gamma beta (positron) Electron Capture big  2 small 2 small  big smoke detectors 14 C dating Cancer therapy PET scan 14 C Bombs + the sun

14. Whence the electron in  -decay?

15. n  p + e  Not an atomic electron! (much more energetic) e.g. : 14 C  14 N + e  6 7 Radiocarbon decay

16. e.g. : 14 N + e    14 C 7 6