Nuclear Chemistry Study Notes

Nuclear Chemistry

Learning Points

  • Nuclear Stability
  • Radioactivity
  • Nuclear Fission and Fusion

Nuclear Stability

  • Refers to the tendency of a nucleus to decay into another element or isotope.
  • The nucleus consists of protons and neutrons, collectively called nucleons:
    • Proton (p)
    • Neutron (n)
    • Electron (e)

Radioactivity

  • Occurs when certain isotopes or nuclides are unstable and emit radiation.
  • Radioactive nuclides spontaneously emit radiation; the atoms containing these are known as radioisotopes.
  • Key Terms:
    • Radioactive Nuclide: An unstable nuclide (
    • Radioisotope: Atoms that contain radioactive nuclides.

Stability Check Criteria

  • To assess if an atom's nucleus is stable or radioactive, compare the number of protons (p⁺) and neutrons (n°).
    • Stable Nuclide Condition:
    • p⁺ = n°
    • Radioactive Condition:
    • p⁺ ≠ n°
    • Mass Number Calculation:
    • Mass Number = Number of Protons + Number of Neutrons
Examples
  • Example 1:
    • 84 208Po:
    • p⁺ = 1, n° ≠ 1 (not stable, radioactive)
  • Example 2:
    • 83 209Bi:
    • p⁺ = 1, n° ≠ 1 (not stable, radioactive)
  • Stability Prediction:
    • Given nuclides:
    • 39 99K: determine whether it is stable or radioactive.
    • 40 19K: determine whether it is stable or radioactive.

Types of Radioactive Decay

  1. Alpha Emission (α)
  2. Beta Emission (β)
  3. Gamma Emission (γ)
  4. Positron Emission (β⁺)
  5. Electron Capture (EC)
Examples of Decay Processes
  • Alpha Decay Example:
    • 226Ra → 222Rn + 4He
  • Beta Decay Example:
    • 14C → 14N + -1e
  • Gamma Decay Example:
    • 99Tc → 99Tc + 0γ
  • Positron Emission Example:
    • 7Be → 7Li + 1e
  • Electron Capture Example:
    • 40K + 0 neutrino → 40Ar + -1e

Rate of Decay

  • Radioactive Decay:
    • The process of disintegration of radionuclides.
  • Decay Rate Formula:
    • Rate = kN, where N is the number of radioactive nuclei at time t, and k is the decay constant.
  • Fraction Remaining:
    • Nt/N0 = e^(-kt), with N0 as the initial amount of nuclei.
  • Detailed derivation of decay constant and half-life:
    • t₁/₂ = ln(2)/k, applies specifically for the time it takes for half of the radioactive material to decay.

Nuclear Reactions: Fission vs Fusion

  • Nuclear Fission:
    • A heavy nucleus splits into lighter nuclei, often involving chain reactions;
    • Controlled for electricity generation, but poses waste disposal issues.
  • Nuclear Fusion:
    • Light nuclei combine to form a heavier nucleus;
    • A cleaner process, yet control mechanisms are still under development.
Nuclear Reactors
  • Serve as the core of nuclear power plants, controlling fission reactions to generate steam and ultimately electricity.
  • Components:
    • Containment structure, steam generator, pressurized water reactor, and fuel rods.

Nuclear Accidents

  • Meltdown: Refers to overheating that may lead to partial or total melting of nuclear core materials, potentially seeping radioactive materials into the environment.
    • Notable event: Chernobyl Disaster

Energy-Mass Equivalence

  • E = mc²: Describes the relationship between mass and energy changes in nuclear reactions, influencing how we understand fission and fusion

Units of Energy in Nuclear Chemistry

  • Basic Energy Units: 1 J = 1 kg m²/s²
    • 1 MeV = 1.602 x 10⁻¹³ J,
    • 1 amu = 931.5 MeV.
Example Calculation
  • For the fusion:
    • 2 1H + 3 1H → 4 2He + 1 1H
    • Calculation of mass defect and energy released during nuclear reactions can be derived from mass values for individual nucleons.