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NUCLEAR CHEMISTRY

NUCLEAR CHEMISTRY. Discovery of Radiation. Roentgen (1895). Studied fluorescent materials that glowed when hit with a beam of electrons.

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NUCLEAR CHEMISTRY

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  1. NUCLEAR CHEMISTRY

  2. Discovery of Radiation Roentgen (1895) • Studied fluorescent materials that glowed when hit with a beam of electrons. • Discovered a mysterious form of radiation was given off even without electron beam. This radiation could pass through paper and other objects but not dense materials (lead, bone). • Called them X-rays

  3. Becquerel (1896) • Studied fluorescent minerals containing uranium. • Discovered radioactivity by accident on a cloudy day: • Thought that an external source was needed to produce the mysterious radiation. • Found that uranium emits radiation without external source.

  4. Pierre and Marie Curie Thought radioactivity was a property of heavy elements. During study, discovered new radioactive elements: Polonium and Radium. Wondered how small mass can give off large amount of energy: Explained by Einstein with E=mc2.

  5. Rutherford • Studied radioactivity and named types of nuclear radiation. • Discovered that elements decay into other elements after emitting nuclear radiation. Called it Nuclear Decay. • Gold foil experiment revealed that the mass of an atom is concentrated in the nucleus (atom is mostly space)

  6. Atomic Structure Recall: Atoms – consist of a positively charged nucleus, which has protons and neutrons. Isotope – atoms of the same chemical element that have a different number of neutrons. Each isotope of a given element is designated by the total number of its protons plus its neutrons. 42 59 101 1 1 2 6 8 14 92 146 238 83 127 210 2 2 4

  7. 4.00260 amu 4.03298 amu Nuclear Forces Mass Defect • Difference between the mass of an atom and the mass of its individual particles.

  8. Nuclear Binding Energy • Energy released when a nucleus is formed from nucleons. • High binding energy = stable nucleus. E = mc2 E: energy (J) m: mass defect (kg) c: speed of light (3.00×108 m/s)

  9. Nuclear Binding Energy Unstable nuclides are radioactive and undergo radioactive decay.

  10. parent nuclide alpha particle daughter nuclide Alpha Emission occurs when the nucleus has too many protons which cause excessive repulsion. Numbers must balance!!

  11. Alpha Emission Ex. Plutonium-239 undergoes alpha decay + = + 239 235 4 Atomic Mass: = + 92 94 2 Atomic #: Masses must be equal = Conservation of mass

  12. Alpha Emission = + 210 A 4 - = = 206 210 4 A + = 2 Z 84 - = = 82 84 2 Z Ex. Polonium-210 undergoes alpha decay to produce this daughter nuclide + Atomic Mass: Atomic #: =

  13. electron Beta Emission occurs when the neutron to proton ratio is too great.

  14. Beta Emission = + 210 A 0 - = = 210 210 0 A + = -1 Z 84 + = = 85 84 1 Z Ex. Polonium-210 undergoes beta decay to produce this daughter nuclide + Atomic Mass: Atomic #: =

  15. Positron Emission positron Occurs when the neutron to proton ratio is too small.

  16. Positron Emission = + 210 A 0 - = = 210 210 0 A + = +1 Z 84 - = = 83 84 1 Z Ex. Polonium-210 undergoes positron emission to produce this daughter nuclide + Atomic Mass: Atomic #: =

  17. electron Electron Capture occurs when the neutron to proton ratio in the nucleus is too small.

  18. Electron Capture + = 210 0 A = 210 A + = -1 Z 84 = 83 Z Ex. Polonium-210 captures an electron to produce this daughter nuclide + Atomic Mass: Atomic #: =

  19. Gamma Emission occurs when the nucleus is at too high an energy. • Emission of high energy electromagnetic wave.

  20. Gamma Emission = + 210 A 0 = 210 A + = 0 Z 84 = 84 Z Ex. Polonium-210 undergoes gamma decay to produce this daughter nuclide + Atomic Mass: Atomic #: =

  21. Nuclear Decay • Transmutation-One element becomes another. • Why nuclides decay • need stable ratio of neutrons to protons More than 83 protons means that the nuclei is unstable (radioactive)

  22. Types of Radiation Charge Shielding 2+ paper • Alpha particle () • helium nucleus • Beta particle (-) • electron 1- lead • Positron (+) • positron 1+ concrete • Gamma () • high-energy photon 0

  23. Penetrating Ability of Radiation

  24. Half-life • Half-life (t½) • Time required for half the atoms of a radioactive nuclide to decay. • Shorter half-life = less stable.

  25. Half-life mf:final mass mi:initial mass n:# of half-lives

  26. Half-life • Fluorine-21 has a half-life of 5.0 seconds. If you start with 25 g of fluorine-21, how many grams would remain after 60.0 s? GIVEN: t½ = 5.0 s mi = 25 g mf = ? total time = 60.0 s n = 60.0s ÷ 5.0s =12 WORK: mf = mi (½)n mf = (25 g)(0.5)12 mf = 0.0061 g

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