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Nuclear Chemistry

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Nuclear Chemistry

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  1. Nuclear Chemistry Chapter 18

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

  3. 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

  4. 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

  5. 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

  6. 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

  7. 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.

  8. 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

  9. 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?

  10. 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?

  11. 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?

  12. Predicting radiation types fromReaction Products • 238U  234Th 234Pa 234U • α β β • 234U  230Th 226Ra  222Rn  218Po  214Pb • α α α α α 214Pb 214Bi 214Po 210Pb 210Bi 210Po206Pb • β β α β β α

  13. Scientists who shaped Nuclear Chemistry • Henri Becquerel 1852- 1908 Discovered Natural Radioactivity - Nobel Prize (physics) 1903 • Wilhem Roentgen 1845- 1923 Discovered X- rays (1895) - Nobel Prize (physics) 1901 • Marie (Sklowdowska) Curie 1867 – 1934 Discovered Radium and Polonium - (2) Nobel Prizes (physics) 1903, Chemistry (1911) – first woman to teach at the Sorbonne in its 650 yr history, first person to receive two Nobel prizes, only person to receive 2 Nobels in Sciences

  14. Scientists who shaped Nuclear Chemistry • Pierre Curie 1859- 1906 Nobel Prize (physics) 1903 • Ernest Rutherford 1871- 1937 Demonstrated the existence of the nucleus Nobel Prize (chemistry) 1908

  15. Medical Applications of Nuclear Chem. • Cancer Radiation Treatment • Computer Imaging techniques • Radiocarbon dating • Smoke detectors • Food irradiation • Radioactive tracers – Iodine 131 used to treat thyroid illnesses and Thallium -201 can be used determine the damage done to someone’s heart by a heart attack

  16. Fission • Nuclear fission was discovered in late 1930’s when U-235 was bombarded with neutrons and observed to split into two lighter elements. • 10n + 23592 U  9236Kr + 14156Ba + 310n • Energy from combustion of 1 mole of U-235 produces 26 million times as much energy as the combustion of 1 mole of methane.

  17. Fission • The neutrons are produced from fission reactions, will then react with other radioactive atoms, which will produce more neutrons and so on, potentially creating an uncontrollable chain reaction.

  18. Critical State of a Fission Reaction • If reaction produces < 1 neutron on average, the nuclear fission stops over time. • If reaction produces exactly 1 neutron for each fission, the process is self-sustaining and is said to be critical. • If reaction produces > 1 neutron from each fission than the process can get out of control very quickly and cause a violent explosion.

  19. Critical Sate of a Fission Reaction • Critical mass = mass of fissionable material needed to keep fission reaction going, but at a safe level. • Hiroshima and Nagasaki bombs in 1945 were fission bombs where two subcritical masses were combined and have an extremely rapid fission reaction that causes a huge explosion.

  20. Sample fission reaction

  21. Nuclear Fusion • Fusion – combining two smaller nuclei into one heavier, more stable nucleus. 32He + 11H  42He + 01e • Fusion reaction produce more energy than fission reactions. • Fusion reactions are most commonly seen in stars.

  22. Nuclear Fusion • We have many potential sources for fusion reactions, but the problem lies in trying to slam two positively charged nuclei together with enough force to make them combine. • It is thought that the temperature must be over 40 million Kelvin for this to occur, which is where the speed of the particles could potentially overcome the repulsive forces.

  23. Sample fusion reaction

  24. Effects of Radiation • Somatic damage – done to the organism itself, resulting in either sickness or death. • Effect of somatic damage may be immediate or take years to show their effects, such as radiation treatment for cancer patients. • Genetic damage – damages cells which can be passed on to afflict offspring of initially effecting organism.

  25. Effects of Radiation • Energy of radiation – higher energy = more damage (big surprise) • Penetrating ability of the radiation – gamma particles are high penetrating, beta can penetrate 1 cm and alpha particles can be stopped by the skin.