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Nuclear Chemistry Chapter 18
Quick Review • Mass # Symbol • Element Name or symbol – Mass # • Parts of a Reaction Reactants Products
Types of Radiation • Alpha emission or decay (a) –helium atom 42He • 23892U 42He + 23490Th • Beta emission or decay (b)– 0-1e in the products • 23490Th 23491Pa + 0-1e • Gamma emission or decay (g) - 00g • 23892U 42He + 23490Th + 00g
Types of Radiation & Particles • Positron emission or decay - 0+1e • 2211Na 0+1e + 2210Ne • Electron capture – beta particle in the reactants • 20180Hg + 0-1e + 20179Au • Neutron emission or decay– 10n • 20984Po 10n + 20084Po • Proton – 11H or 11p
Balancing Nuclear Equations • Mass # and the atomic # totals must be the same for reactants and the products. • 3919K 3517Cl + ___ • 20682Pb 0-1e + ___ • 23894Pu + ___ 42He + 23592U
Writing Balanced Nuclear Equations • 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
Half-Life and Nuclear Stability • 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.
Sample Half-lives • IsotopesHalf-Live • Carbon – 14 5730 years • Sodium – 24 15 hours • Bismuth – 212 60.5 seconds • Polonium – 215 0.0018 seconds • Thorium – 230 75400 years • Thorium – 234 24.1 days • Uranium – 235 7.0 x 108 years • Uranium – 238 4.46 x 109 years
Half-life sample problems • 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?
Half-life sample problems • How many days will it take 50 grams of Radon – 222 (half-life of 3.82 days) to decay to 3.125 grams?
Half-life sample problems • 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?
Fission versus Fusion • Fusion – combining two smaller nuclei into one heavier, more stable nucleus. 32He + 11H 42He + 01e • Fission – splitting a large unstable nucleus into two nuclei with smaller mass numbers. 20984Po 12552Te + 8432Ge