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CHAPTER 28 Nuclear Chemistry

CHAPTER 28 Nuclear Chemistry . Radioactive Decay. A. Nuclear Stability. Nuclide = atom of an isotope. A . Nuclear Stability. Nuclear stability – stable nuclei always have at least as many neutrons as protons. A. Nuclear Stabiity.

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CHAPTER 28 Nuclear Chemistry

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  1. CHAPTER28Nuclear Chemistry Radioactive Decay

  2. A. Nuclear Stability • Nuclide = atom of an isotope

  3. A. Nuclear Stability • Nuclear stability – stable nuclei always have at least as many neutrons as protons.

  4. A. Nuclear Stabiity • For an odd/even or even/odd nucleus, if the mass number is different by more than 1 amu from the rounded atomic mass, the nuclide is unstable. • Ex:

  5. A. Nuclear Stability • For an even/even nucleus, if the mass number is different by more than 3 amu from the rounded atomic mass, the nuclide is unstable. • Ex:

  6. A. Nuclear Stability • For odd/odd nuclei, only four stable isotopes are found in nature:

  7. B. Nuclear Decay • Alpha particle () • helium nucleus paper 2+ • Beta particle (-) • electron 1- lead • Positron (+) • positron 1+ concrete • Gamma () • high-energy photon 0

  8. parent nuclide alpha particle daughter nuclide B. Nuclear Decay • Alpha Emission Top and bottom numbers must balance!!

  9. electron positron B. Nuclear Decay • Beta Emission • Positron Emission

  10. electron B. Nuclear Decay • Electron Capture • Gamma Emission • Usually follows other types of decay. • Transmutation • Atom of one element changes into an atom of another element.

  11. B. Nuclear Decay • Why nuclides decay… • need stable ratio of neutrons to protons DECAY SERIES TRANSPARENCY

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

  13. D. Radiocarbon Dating • Carbon-14 is in all living things through the carbon cycle. • Amount of carbon-14 stays constant until organism dies, then it begins to decay.

  14. D. Radiocarbon Dating • Amount of carbon-14 can be expressed as either a percentage or as a decimal number. • Example: amount of carbon-14 in a dead tree could be expressed as 38% or 0.38 of the original amount.

  15. D. Radiocarbon Dating • Half-life of carbon-14 : 5730 years

  16. E. Fission • Occurs when isotopes are bombarded with neutrons and split the nucleus into smaller fragments, accompanied by the release of neutrons and a large amount of energy. (Each atom can capture 1 neutron.)

  17. E. Fission • Chain reaction – occurs when atomic nuclei that have split release energetic neutrons that split more nuclei.

  18. E. Fission • Two steps in controlling fission: • Neutron moderation – water or carbon slows down the neutrons • Neutron absorption – decreases the number of slow neutrons through the use of control rods made of neutron-absorbing materials (usually cadmium)

  19. F. Fusion • Occurs when two light nuclei combine to produce a nucleus of heavier mass, accompanied by the release of a large amount of energy.

  20. F. Fusion • Occurs in all stars • High temperatures are necessary to initiate fusion (no cold fusion yet) • Possible future energy source • Hydrogen bomb is a fusion reaction (fusion of two deuterium nuclei).

  21. G. Methods of Detection • Geiger Counters (primarily beta) • Scintillation counter – coated screen detects radiation particles. • Film badge – several layers of photographic film encased in a holder. Detects beta and gamma.

  22. H. Radioisotopes in Medicine • X-rays: Useful in imaging soft-tissue organs. • Tracers: Iodine-131 is used to check for thyroid problems • Radiation treatment: Some cobalt isotopes are used as radiation sources to treat cancer.

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