1. N UCLEAR C HEMISTRY C HEMISTRY INVOLVING CHANGES IN THE NUCLEUS R EFERENCES : T EXT C HAPTER 19 R EVIEW B OOK T OPIC 12

2. T HE N UCLEUS Remember that the nucleus is comprised of protons and neutrons. The number of protons is the atomic number. The number of protons and neutrons together is the mass of the atom.

3. I SOTOPES Not all atoms of the same element have the same mass due to different numbers of neutrons in those atoms. There are three naturally occurring isotopes of uranium: Uranium-234 Uranium-235 Uranium-238

4. S TABLE N UCLEI The shaded region in the fig. shows what nuclides would be stable, the so-called belt of stability. It is the ratio of neutrons to protons that determines the stability of a given nucleus.

5. R ADIOACTIVITY It is not uncommon for some nuclei to be unstable, or radioactive. There are no stable nuclei with an atomic number greater than 83. Radioisotopes = isotopes that are unstable and thus radioactive There are several ways radionuclides can decay into a different nuclide ** a nuclide is a nucleus with a specified number of protons and neutrons

6. R ADIOACTIVE S ERIES Large radioactive nuclei cannot stabilize by undergoing only one nuclear transformation. They undergo a series of decays until they form a stable nuclide (often a nuclide of lead). Transmutation = the reaction by which the atomic nucleus of one element is changed into the nucleus of a different element

7. T YPES OF R ADIOACTIVE D ECAY A LPHA D ECAY = Loss of an  -particle (a helium nucleus) He 4242 U 238 92  Th 234 90 He 4242 + Atomic # decreases by 2 Mass # decreases by 4 # of protons decreases by 2 # of neutrons decreases by 2

8. T YPES OF R ADIOACTIVE D ECAY B ETA D ECAY = Loss of a  -particle (a high energy electron)  0−10−1 e 0−10−1 or I 131 53 Xe 131 54  + e 0−10−1 Atomic # increases by 1 # of protons increases by 1 # of neutrons decreases by 1 Mass # remains the same

9. T YPES OF R ADIOACTIVE D ECAY P OSITRON E MISSION = Loss of a positron (a particle that has the same mass as but opposite charge than an electron) e 0101 C 11 6  B 11 5 + e 0101 Atomic # decreases by 1 # of protons decreases by 1 # of neutrons increases by 1 Mass # remains the same

10. T YPES OF R ADIOACTIVE D ECAY G AMMA E MISSION = Loss of a  -ray (a photon of high-energy light that has no mass or charge & that almost always accompanies the loss of a nuclear particle; often not shown when writing nuclear equations)  0000

11. Table N shows the decay mode of selected radioisotopes

12. A RTIFICIAL T RANSMUTATION = done by bombarding the nucleus with high- energy particles (such as a neutron or alpha particle), causing transmutation 40 20 Ca + _____ -----> 40 19 K + 1 1 H 96 42 Mo + 2 1 H -----> 1 0 n + _____ **Natural transmutation has a single nucleus undergoing change, while artificial transmutation will have two reactants (fast moving particle & target nuclei.**

13. N UCLEAR F ISSION Nuclear fission is the type of reaction carried out in nuclear reactors. = splitting of large nuclei into middle weight nuclei and neutrons

14. N UCLEAR F ISSION Bombardment of the radioactive nuclide with a neutron starts the process. Neutrons released in the transmutation strike other nuclei, causing their decay and the production of more neutrons. This process continues in what we call a nuclear chain reaction.

15. = the combining of light nuclei into a heavier nucleus 2 1 H + 2 1 H  4 2 He + energy Two small, positively-charged nuclei smash together at high temperatures and pressures to form one larger nucleus. Nuclear Fusion

16. H ALF -L IFE = the time it takes for half of the atoms in a given sample of an element to decay - Each isotope has its own half-life; the more unstable, the shorter the half-life. - Table N: Selected radioisotopes - Table T: Equations : fraction remaining = (1/2) (t/T) # of half-lives remaining = t/T Key: t = total time elapsed T = half-life HALF LIFE

17. S AMPLE H ALF -L IFE Q UESTION Most chromium atoms are stable, but Cr-51 is an unstable isotope with a half-life of 28 days. What fraction of a sample of Cr-51 will remain after 168 days? How can we solve this problem? What information do we need?

18. S AMPLE H ALF -L IFE Q UESTION If a sample of Cr-51 has an original mass of 52.0g, what mass will remain after 168 days?

19. S AMPLE H ALF -L IFE Q UESTION How much was present originally in a sample of Cr-51 if 0.75g remains after 168 days?

20. S OME PRACTICAL USES OF R ADIOISOTOPES ( DATING, CHEMICAL TRACERS, INDUSTRIAL APPLICATIONS, MEDICAL APPLICATIONS, NUCLEAR POWER PLANTS ) Medical Uses 60 Co (cobalt-60) used in cancer treatments and used to kill bacteria in food products 226 Ra (Radium-226) used in Cancer treatment 131 I diagnosis and treatment of thyroid disorders 11 C Positron emission tomography (PET scans) Other Uses 14 C archaeological dating (of once living things) and organic compounds 238 U archaeological dating (U-238 to Pb-206 ratio) 241 Am (Americium-241) smoke detectors 235 U nuclear reactors and weapons