Chapter 18

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

 Alpha emission or decay (  ) –helium atom 4 2 He  U  4 2 He Th  Beta emission or decay (  )– 0 -1 e in the products  Th  Pa e  Gamma emission or decay (  )   U  4 2 He Th 

 Positron emission or decay e  Na  0 +1 e Ne  Electron capture – beta particle in the reactants  Hg e  Au  Neutron emission or decay– 1 0 n  Po  1 0 n Po  Proton – 1 1 H or 1 1 p

 Mass # and the atomic # totals must be the same for reactants and the products.  K  Cl + ___  Pb  0 -1 e + ___  Pu + ___  4 2 He U

 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

 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.

 IsotopesHalf-Live  Carbon – years  Sodium – 2415 hours  Bismuth – seconds  Polonium – seconds  Thorium – years  Thorium – days  Uranium – x 10 8 years  Uranium – x 10 9 years

 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? 

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

 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?

 Fusion – combining two smaller nuclei into one heavier, more stable nucleus. 3 2 He H  4 2 He e  Fission – splitting a large unstable nucleus into two nuclei with smaller mass numbers Po  Te Ge