Chapter 21: Nuclear Chemistry

21.1 Radioactivity and Nuclear Equations

Review of Isotopes

• Mass Number: Total number of protons and neutrons.
• Atomic Number: Number of protons.
• Nucleus contains:
  • Protons: +1 charge
  • Neutrons: No charge

Isotopes

• Atoms of the same element with different masses due to different numbers of neutrons.
• Example: Uranium isotopes - Uranium-234, Uranium-235, Uranium-238.
• Radioactive nuclei emit radiation and are called radionuclides.

Nuclear Equations

• Nuclear Reactions: Affect the nucleus, must balance atomic and mass numbers, unlike chemical reactions.

Properties of Radioactive Decay

• Types of Radiation:
  • Alpha (α): Charge +2, low penetration, helium nucleus.
  • Beta (β): Charge -1, more penetration, high-speed electrons.
  • Gamma (γ): No charge, high penetration, high-energy photons.

Types of Decay

• Alpha Decay: Loss of an alpha particle (He nucleus).
• Beta Decay: Loss of a beta particle (electron).
• Gamma Decay: Loss of a high-energy photon, often accompanies other decays.
• Positron Emission: Proton converts to neutron, positron emitted.
• Electron Capture: Electron absorbed by the nucleus, converts proton to neutron.

Nuclear Reaction Changes

• Beta Emission: Neutron to proton.
• Positron Emission & Electron Capture: Proton to neutron.

21.2 Patterns of Nuclear Stability

Stability Forces

• Strong Nuclear Force: Binds nucleus despite proton-proton repulsion.
• Balance of protons and neutrons is key.

Stability Indicators

• Proton/Neutron Ratio: 1:1 for smaller nuclei, more neutrons needed for larger nuclei.
• Belt of Stability: Represents stable nuclides.
• Unstable Nuclei:
  • Above belt: Too many neutrons, decay by beta emission.
  • Below belt: Too many protons, decay by positron emission or electron capture.
  • Large atomic numbers (>83): Alpha decay.

Radioactive Decay Chains

• Series of decays required to reach a stable nuclide, often ending in lead.

"Magic Numbers" for Stability

• Certain numbers of protons/neutrons provide extra stability, favoring even numbers.

21.3 Nuclear Transmutations

Nuclear Transmutations

• Occur when nuclei collide with other particles (e.g., nuclei or neutrons).

Particle Accelerators

• Linear accelerators, cyclotrons, synchrotrons used to speed up particles for collisions.

Creation of Synthetic Isotopes

• Neutrons used for creating isotopes for medical use.
• Transuranium elements (>92) created by bombarding with neutrons.

21.4 Kinetics of Radioactive Decay

Decay Kinetics

• First-order processes.
• Half-Life: Time for half a sample to decay.

Radiometric Dating

• Uses decay information to date objects, e.g., carbon dating (C-14).

Measuring Radioactivity

• Units: Becquerel (Bq), Curie (Ci).

Detection Methods

• Film badges, Geiger counters, scintillation counters.

Medical Applications

• Radiotracers: Used in diagnostics (e.g., PET scans).

21.5 Energy Changes in Nuclear Reactions

Mass-Energy Equivalence

• E=mc²: Mass defect contributes to nuclear binding energy.

Fission vs Fusion

• Fission: Splits heavy nuclei, releases energy.
• Fusion: Combines light nuclei, requires high energy, releases more energy.

21.7 Nuclear Power

Fission Power

• Nuclear reactors use controlled fission to generate energy.
• Components: Fuel rods, control rods, coolant.

Fusion Power

• Produces no radioactive by-products, requires extreme conditions.

21.9 Radiation in the Environment

Ionizing Radiation

• Causes radical formation, affects DNA/RNA.

Biological Impact

• Type and location of exposure determine damage severity.
• External vs internal radiation risks.

Radiation Dose Measurement

• Units: Gray (Gy), Rad.
• Biological effectiveness measured by RBE (relative biological effectiveness).

Short-Term Exposure Effects

• Ranges from no effect to fatal, depending on dose (rem).