Nuclear Chemistry Notes

  • Study of the structure of atomic nuclei and the changes they undergo.

  • Characteristics of nuclear reactions: Isotopes change into isotopes of another element, contents of the nucleus change, and large amounts of energy are released.

Chemical Vs. Nuclear Reactions

Chemical Reactions

  • Bonds are broken and formed.

  • Atoms are rearranged.

  • Involves valence electrons from the electron cloud.

  • Small energy changes.

Nuclear Reactions

  • Nuclei emit particles and/or rays.

  • Atoms often change into atoms of a different element.

  • Involves protons, neutrons, and/or electrons from the nucleus.

  • Large energy changes.

Radioactivity

  • Process by which atoms give off rays or particles.

  • Radiation refers to the penetrating rays and particles emitted by a radioactive source.

The Discovery of Radioactivity (1895 – 1898)

  • Roentgen discovered x-rays when electrons hit a fluorescent screen.

  • Becquerel discovered radioactivity through uranium rocks on photographic plates.

  • Marie and Pierre Curie isolated components of uranium and identified polonium and radium, contradicting Dalton's theory of indivisible atoms.

Review of Atomic Structure

Nucleus

  • Majority of mass (99.9%) of the atom.

  • Contains protons (positively charged) and neutrons (neutral).

Electron Cloud

  • Majority of volume of the atom (9,999 times the size of the nucleus).

  • Contains electrons (negatively charged).

Forces in the Atom

  • Strong nuclear force holds protons and neutrons together.

  • Weak electrostatic force acts between electrons and the nucleus.

Atomic Terms

  • Nucleons: Particles in the nucleus (neutrons and protons).

  • Nuclear Symbol: Consists of the element symbol, atomic number (Z), and mass number (A).

  • Nuclide: Each unique atom.

  • Ion: An atom with a charge.

Isotopes and Radioisotopes

  • Isotopes: Atoms of the same element with different numbers of neutrons.

  • Radioisotopes: Unstable isotopes with too many or too few neutrons.

  • Radioactive decay: Process by which unstable nuclei emit radiation to become more stable.

Nuclear Stability

  • Elements with atomic numbers 1 to 20 are generally stable with a 1:1 ratio of protons to neutrons.

  • Elements 21 to 83 are marginally stable with a 1:1.5 ratio.

  • Elements greater than atomic number 83 are unstable and radioactive, typically having more neutrons than protons.

Types of Nuclear Reactions

  1. Radioactive Decay: Emission of alpha, beta particles, and gamma rays.

  2. Nuclear Disintegration: Emission of protons or neutrons.

  3. Transmutation: Converting an atom of one element into another, usually through radioactive decay.

Nuclear Equations

  • Show the radioactive decomposition of elements (e.g., 14C → 14N + 0).

Alpha Radiation

  • Composition: Alpha particles (helium nuclei).

  • Charge: 2+; low penetrating power (0.05 mm body tissue).

  • Shielding: Paper or clothing.

  • Uses: Cancer treatment, smoke detectors.

Alpha Decay Examples

  • Polonium-210 decays to lead-206 via alpha emission.

  • Radium-226 decays to radon-222 via alpha emission.

Beta Radiation

  • Composition: Beta particles (fast-moving electrons).

  • Charge: 1-; moderate penetrating power (4 mm body tissue).

  • Shielding: Metal foil.

  • Uses: PET scans, tracers for biological research.

Beta Decay Examples

  • Carbon-14 decays to nitrogen-14 via beta emission.

  • Zirconium-97 decays to niobium-97 via beta decay.

Gamma Radiation

  • Composition: High-energy electromagnetic radiation.

  • Charge: 0; high penetrating power (penetrates body easily).

  • Shielding: Lead, concrete, water.

  • Uses: Radiation therapy, medical scanning.

Half-Life

  • Time required for half of a radioisotope's nuclei to decay.

  • Represented as t1/2.

  • Longer half-lives indicate more stable isotopes.

  • Used for radioactive dating (e.g., Carbon-14).

Half-Life Example Calculations

  1. Strontium-90 decay over 116 years: Initial 10.0 g → Remaining 0.625 g.

  2. Gallium-68 decay after 3 half-lives: Initial 160.0 mg → Remaining 20.0 mg.

  3. Cobalt-60 decay after 15 years (3 half-lives): Initial 30.0 g → Remaining 3.75 g.

Nuclear Fission

  • Splitting of a nucleus releasing a large amount of energy.

  • Produces radioactive waste; examples include atomic bombs and reactors.

Nuclear Fusion

  • Combining of two light nuclei into a heavier nucleus, releasing more energy than fission.

  • No radioactive waste; examples include reactions in stars and hydrogen bombs.

Advantages and Disadvantages of Fission and Fusion

Advantages of Fission

  • Zero air pollution; contributes less to climate change.

  • Can be controlled.

Disadvantages of Fission

  • High-level radioactive waste.

  • Potential for catastrophic failures (Chernobyl, Fukushima).

Advantages of Fusion

  • No radioactive waste.

  • Very large energy output.

Disadvantages of Fusion

  • Requires large energy input to initiate.

  • Difficult to control.