1. Chapter 18

2.  Mass # Symbol  Element Name or symbol – Mass #  Parts of a Reaction Reactants  Products

3.  Alpha emission or decay (  ) –helium atom 4 2 He  238 92 U  4 2 He + 234 90 Th  Beta emission or decay (  )– 0 -1 e in the products  234 90 Th  234 91 Pa + 0 -1 e  Gamma emission or decay (  ) - 0 0   238 92 U  4 2 He + 234 90 Th + 0 0 

4.  Positron emission or decay - 0 +1 e  22 11 Na  0 +1 e + 22 10 Ne  Electron capture – beta particle in the reactants  201 80 Hg + 0 -1 e  + 201 79 Au  Neutron emission or decay– 1 0 n  209 84 Po  1 0 n + 200 84 Po  Proton – 1 1 H or 1 1 p

5.  Mass # and the atomic # totals must be the same for reactants and the products.  39 19 K  35 17 Cl + ___  206 82 Pb  0 -1 e + ___  238 94 Pu + ___  4 2 He + 235 92 U

6.  Alpha decay of Cu-68  Gamma emission of Thorium-235  Positron emission of P-18  Astatine-210 releasing 3 neutrons  Electron capture of Ti-45

7.  Radioactive isotopes or nuclides all decay because they are unstable, some just breakdown much faster than others  Half-life – amount of time for half of the original sample to decay  For two samples of the same isotope, regardless of the sample size, after one half- life, only half of the original amount of sample remains.

8.  IsotopesHalf-Live  Carbon – 145730 years  Sodium – 2415 hours  Bismuth – 21260.5 seconds  Polonium – 215 0.0018 seconds  Thorium – 23075400 years  Thorium – 23424.1 days  Uranium – 2357.0 x 10 8 years  Uranium – 2384.46 x 10 9 years

9.  Barium – 139 has a half-life of 86 minutes. If you originally have a 10 gram sample of Barium-139, how much will be left after 258 minutes? 

10.  How many days will it take 50 grams of Radon – 222 (half-life of 3.82 days) to decay to 3.125 grams?

11.  If a sample of Cesium-135 decays from 10 grams to 2.5 grams over a period of 84 days, what is the half-life of Cesium-135?

12.  Fusion – combining two smaller nuclei into one heavier, more stable nucleus. 3 2 He + 1 1 H  4 2 He + 0 1 e  Fission – splitting a large unstable nucleus into two nuclei with smaller mass numbers. 209 84 Po  125 52 Te + 84 32 Ge