Chapter 5: Nuclear Chemistry

Introduction to Nuclear Chemistry

Nuclear chemistry explores the behavior of atomic nuclei, including their stability, radioactive decay, and applications in medicine and energy. It is a fundamental topic in General, Organic, and Biological (GOB) Chemistry, with direct relevance to health, environmental science, and technology.

Natural Radioactivity

Radioactive Isotopes and Stability

Atoms with unstable nuclei spontaneously emit radiation to become more stable. These atoms are called radioisotopes. Most elements up to atomic number 19 have stable nuclei, while elements with atomic numbers 20 and higher often have unstable isotopes.

• Radioisotope: An isotope with an unstable nucleus that emits radiation.

• Example: Carbon-14 (146C) is used in archaeological dating.

Stable vs. Radioactive Isotopes

Isotopes are classified as stable or radioactive based on their nuclear properties. The mass number and atomic number are used to identify isotopes.

Types of Radiation

Alpha, Beta, Positron, and Gamma Radiation

Radioisotopes emit different types of radiation:

• Alpha (α) particles: Identical to a helium nucleus (42He), low energy, charge +2.

• Beta (β) particles: High-energy electrons (0-1e), charge -1.

• Positrons (β+): Positive electrons (0+1e), charge +1.

• Gamma (γ) rays: Pure energy (00γ), no charge or mass.

Alpha Decay

Alpha decay occurs when a nucleus emits an alpha particle, decreasing its mass number by 4 and atomic number by 2.

• Example: Uranium-238 decays to thorium-234 by emitting an alpha particle.

Beta Decay

Beta decay occurs when a neutron in the nucleus converts to a proton and emits a beta particle, increasing the atomic number by 1.

• Example: Carbon-14 decays to nitrogen-14 by emitting a beta particle.

Positron Emission

Positron emission occurs when a proton converts to a neutron and emits a positron, decreasing the atomic number by 1.

Summary of Radiation Types

Each type of radiation results in a new nucleus with specific changes to mass and atomic numbers.

Biological Effects and Protection

Biological Effects of Radiation

Ionizing radiation damages rapidly dividing cells, including bone marrow, skin, reproductive organs, and cancer cells. Large doses are used to destroy cancer cells, but can also cause genetic mutations and other health issues.

Radiation Protection

Different types of radiation require specific shielding:

• Alpha: Paper, clothing

• Beta: Heavy clothing, lab coats, gloves

• Gamma: Lead, thick concrete

Nuclear Reactions and Equations

Writing Nuclear Equations

Nuclear equations show the changes in mass and atomic numbers during radioactive decay. The sum of mass numbers and atomic numbers must be equal on both sides of the equation.

• Alpha decay:

• Beta decay:

• Positron emission:

Production of Radioactive Isotopes

Bombardment Reactions

Radioisotopes can be produced by bombarding stable nuclei with particles such as alpha particles, protons, or neutrons.

• Example:

Radiation Measurement

Detection and Units

Radiation is detected using instruments such as Geiger counters and dosimeters. Key units include:

• Curie (Ci): Activity, 1 Ci = disintegrations/s

• Becquerel (Bq): SI unit, 1 Bq = 1 disintegration/s

• Rad: Absorbed dose

• Rem: Biological damage

• Sv (Sievert): SI unit for biological damage, 1 Sv = 100 rem

Half-Life of Radioisotopes

Definition and Calculation

The half-life is the time required for half of the radioactive atoms in a sample to decay. It is used to determine the age of objects and the remaining activity of radioisotopes.

• Decay curve: Shows the decrease in radioactivity over time.

• Formula: , where is the number of half-lives.

Applications of Radioactivity

Medical Applications

Radioisotopes are used in diagnosis and treatment of diseases. Short half-life isotopes are preferred for medical imaging and therapy.

• Examples: Tc-99m for imaging, I-131 for thyroid treatment, F-18 for PET scans.

Environmental and Archaeological Applications

Radioisotopes are used for dating ancient objects, such as bones and artifacts, using carbon-14 dating.

Nuclear Fission and Fusion

Nuclear Fission

Fission is the splitting of a large nucleus (e.g., U-235) into smaller nuclei, releasing energy and neutrons. It is the basis for nuclear reactors and atomic bombs.

• Equation:

• Chain reaction: Neutrons produced can cause further fission events.

Nuclear Fusion

Fusion combines small nuclei (e.g., hydrogen isotopes) to form larger nuclei (e.g., helium), releasing even more energy. Fusion occurs in stars and is a potential energy source with less radioactive waste.

• Equation:

Summary Table: Properties of Radiation and Shielding

Summary Table: Units of Radiation Measurement

Summary Table: Half-Lives of Common Radioisotopes

Key Equations

• Einstein's Mass-Energy Relation:

• Half-life calculation:

• Radiation dose:

Concept Map

Nuclear chemistry connects atomic structure, radioactivity, nuclear reactions, measurement, and applications in medicine and environmental science.

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