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Nuclear Chemistry

Nuclear Chemistry. Ch.18. (18-1) Nuclear Stability. Nucleons : p + & n 0 Nuclide : any combo of p + & n 0 in a nucleus Isotope : same at.#, but different mass Te-122, Te-124, Te-128 Isobar : same mass, but different at.# Xe-124, Te-124, Sn-124. Binding Forces.

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Nuclear Chemistry

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  1. NuclearChemistry Ch.18

  2. (18-1) Nuclear Stability • Nucleons: p+ & n0 • Nuclide: any combo of p+ & n0 in a nucleus • Isotope: same at.#, but different mass • Te-122, Te-124, Te-128 • Isobar: same mass, but different at.# • Xe-124, Te-124, Sn-124

  3. Binding Forces • Strong nuclear force: attraction that holds nuclear particles together • Overcomes repulsive forces

  4. Mass Defect • Mass converted to E when a nucleus forms

  5. Nuclear Binding E • E emitted when nucleons come together (E needed to break a nucleus apart)

  6. Band of Stability • Area on a graph of n0 # v. p+ # in which all stable nuclei lie

  7. Nuclei are more stable if they… • Contain n0 ≥ p+ • Do not have too many or too few n0 • Have even #’s of nucleons • Have “magic #’s” of p+ or n0 • 2, 8, 20, 28, 50, 82, 126 • Are not a neighboring isobar

  8. (18-2) Types of Nuclear Change • Spontaneous • Radioactivity • Artificial Transmutations 2. Fission 3. Fusion • Nonspontaneous 4. Transmutation

  9. Radioactivity • A nucleus decays & emits particles & electromagnetic waves

  10. Converting n0 to p+ • Beta (β) decay: nuclei w/ too many n0 for the at.# become more stable by decaying & emitting radiation • β particle: e- emitted from a nucleus when a n0 changes to a p+ • Ex:

  11. Converting p+ to n0 • e- capture: nucleus has too few n0, so it absorbs an e-, which changes a p+ into a n0 • Gamma rays (γ): E produced by decaying nuclei • Ex:

  12. Converting p+ to n0 (cont.) • Positron emission: nuclei emit postitrons (antiparticles of e-) • Ex:

  13. Annihilation of Matter • Event when a particle collides w/ its anitparticle & both are changed into E

  14. Losing Alpha Particles • Alpha (α) decay: very large nuclei w/ too few n0 can decay by emitting α particles • α particles: Helium-4 made when a n0 decays • Ex: • Decay series: many heavy nuclei must decay several times before reaching a stable state

  15. Balancing Nuclear Eq.’s • Total mass #’s & nuclear charges must balance on both sides of the eq. • Ex: Masses = 234, Charges = 90 • Ex: Masses = 238, Charges = 92

  16. Nuclear Fission • Rxn in which a large nucleus splits into 2 & produces a lot of E • Chain rxn: nuclear rxn that sustains itself • Critical mass: smallest mass of radioactive material needed to sustain a chain rxn

  17. Nuclear Fusion • 2 small nuclei combine to form 1 more stable nucleus & lots of E • Reactants are plasmas (mixture of + nuclei & e-) • Need very high T’s & P’s

  18. Transmutation • Creating new nuclei by bombarding a nucleus w/ α particles • Produces an unstable cmpd that stabilizes by emitting a p+

  19. (18-3) How Nuclear Chem is Used • Radioactive dating: using radioactive isotopes to determine an object’s age • Half-life: time required for half of a radioactive material to decay

  20. Smoke Detectors • Have an α emitter, which attract e- from the gas, changing them to ions which conduct electricity • When smoke particles mix w/ the gas, they reduce current flow & the detector’s circuits are set off

  21. Neutron Analysis • Used to determine composition of objects • Meteorite composition • Forensic science (gun residue)

  22. Radiation Exposure • rem: biological effect of exposure to nuclear radiation • Limit of 5 rems/yr

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