Nuclear Chemistry

• Elements undergo chemical changes so it can become more stable.

• Stability depends on the proton to neutron ratio.

  • Atomic numbers < 20 are the most stable because the ratio is about 1:1

• Henri Becquerel called emission from decay uranic rays because they were emitted from uranium.

• Marie Curie discovered Po (Polonium) and Ra (Radon) which emitted uranic rays, changing uranic rays to radioactivity.

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Radioactivity: emission of subatomic particles or high energy electromagnetic radiation by nuclei. such atoms/isotopes said to be radioactive

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Nuclear Decay:

• protonsnucleons, (neutrons + protons)X

• An unstable nucleus undergoes a change and reduction in energy to become more stable.

• The four types of nuclear decay (+ gamma)

  • Alpha decay
  • largest ionizing power, lowest penetrating power
  • can penetrate matter
  • nucleus emits alpha particle
  • # nucleons must =, # protons must =
  • 24He is the alpha particle. It is always one of the daughter particles.
  • Beta decay
  • high speed electron is ejected from a nucleus
  • turns neutron into proton
  • it has a lower ionizing power than alpha particle but a higher penetration power
  • Positron emission
  • positron is antiparticle of e
  • collision with e causes gamma ray emission
  • cause: too little neutrons
  • proton converted into neutron, emits positron
  • Gamma decay
  • electromagnetic radiation
  • high-energy photons
  • no charge, no mass
  • usually emitted in conjunction with other radiation types
  • lowest ionizing power, highest penetrating power
  • requires several inches lead shielding
  • Electron capture
  • particle absorbed by unstable nucleus
  • converts proton into neutron
  • different from beta decay! 2 reactants, 1 product

• Nuclear decay series:

  • Uranium has an atomic number greater than 83. Therefore it is naturally radioactive.
  • Uranium decays into Thorium by alpha decay.
  • Thorium decays into Protactinium by alpha decay.
  • Protactinium decay next and so on until we reach a stable non-reactive element.

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Nuclear half-life:

• Unstable nuclei emit either an alpha, beta, or positron particle to try to shed mass or improve their neutron to proton ratio.
• You cannot predict when an oculus will disintegrate for individual nuclei, but you can when you look at large # of atoms.
• The half-life of any nuclide does not depend on temperature, pressure, or amount of material left. It depends on the N/P ratio.
• Loss of mass to decay
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