Intro Chem Chapter 9 Study Notes

Introduction

  • Study of nuclear chemistry and its principles.

Chapter Overview: Nuclear Chemistry

  • Focuses on properties of atomic nuclei and nuclear radiation.

Nuclear Radiation

  • Definition: Radiation emitted from a nucleus during decay.

  • Types of Nuclear Radiation:

    • Alpha Particle (α):

      • Helium nucleus (He²⁺)

      • Contains 2 protons and 2 neutrons.

      • Mass: 4 amu;

      • Atomic number: 2.

    • Beta Particle (β-):

      • An electron with a charge of -1.

      • Mass: 0.00055 amu.

    • Positron (β+):

      • Similar mass to an electron (0.00055 amu) but with a +1 charge.

    • Gamma Ray (γ):

      • High-energy electromagnetic radiation.

Electromagnetic Radiation

  • All forms differentiate by wavelength (λ) and frequency (ν).

  • Frequency: Number of crests passing a point per second; higher frequency = shorter wavelength & higher energy.

Natural and Artificial Isotopes

  • Over 300 naturally occurring isotopes;

    • 264 are stable; rest are radioactive.

  • Stable isotopes have similar numbers of protons and neutrons in lighter elements.

  • Heavier elements require more neutrons (e.g., Lead-206).

  • Over 1000 artificial isotopes exist; all are radioactive.

Beta Emission

  • Process: A neutron converts into a proton and an electron, emitting the electron (beta particle).

  • Result: Element stays the same mass but increases atomic number by one.

    • Example: Phosphorus-32 is a beta emitter.

  • Problem Example:

    • Carbon-14 beta emission converts to Nitrogen-14.

Alpha Emission

  • Process: Emission of a helium nucleus (alpha particle).

  • Resulting element has atomic number reduced by 2 and mass number reduced by 4.

Positron Emission

  • Emission of a positron from the nucleus; new element has atomic number decreased by 1, mass number unchanged.

Gamma Emission

  • No change in atomic or mass number; high-energy state returns to ground state by emitting gamma radiation.

Electron Capture

  • An electron captured by a nucleus replaces a proton, forming a neutron; atomic number decreases, mass number remains unchanged.

Half-Life

  • Definition: Time taken for half the sample of a radioisotope to decay.

  • Example:

    • Iodine-131 half-life is 8 days; decays through beta and gamma emission.

Characteristics of Nuclear Radiation

  • Intensity Measurement:

    • Instruments like Geiger-Müller counters for ionization measurement.

    • Scintillation counters emit light when struck by radiation; measured in counts/min or counts/s.

Radia tion Dosimetry Overview

  • Alpha particles, though damaging, have low penetration; harmful if ingested.

  • Beta particles penetrate more and are more harmful.

  • Gamma rays are highly penetrating and most dangerous.

Radiation Dosimetry Terms and Units

  • Becquerel (Bq): 1 dps (disintegration/second).

  • Curie (Ci): Equivalent of 3.7 x 10¹⁰ dps.

  • Roentgen (R): Measures ionizing energy delivered from a source; 1 R = 2.58 x 10⁻⁴ coulomb/kg.

  • Gray (Gy): SI unit for absorbed dose; 1 Gy = 100 rad.

  • Sievert (Sv): SI unit for measuring radiation effect on humans; 1 Sv = 1 rad.

Average Exposure and Effects of Radiation

  • Average exposure from natural and artificial sources total approximately 359 mrem/year.

  • Health Effects:

    • 25 rem: Decreased white blood cell count.

    • 100 rem: Symptoms of radiation sickness.

    • 400 rem: 50% fatality in a month.

    • 600 rem: Almost invariably lethal within a month.

    • 50,000 rem needed to kill bacteria.

Nuclear Medicine

  • Application of nuclear chemistry principles in medical treatments and diagnostics.

Nuclear Fusion

  • Definition: Combining of hydrogen nuclei to form helium, releasing energy as photons.

  • Essential for creating transuranium elements.

  • Fusion of deuterium and tritium releases a large amount of energy through mass decrease.

Nuclear Fission

  • Definition: Splitting of larger nuclei into smaller ones; significant energy release due to mass decrease.

  • Initiated when uranium-235 is bombarded with neutrons.

  • Over 20% of U.S. electricity is generated through nuclear power; responsible disposal of spent fuel is crucial.

Conclusion

  • Understanding nuclear processes, including fission and fusion, is essential for advancements in nuclear chemistry and applications in energy and medicine.