6.7 Chemical Building Blocks

6.7.1 Summary of Chemical Building Blocks

• Atoms:
    - Definition: The smallest units of matter that retain the properties of an element.
    - Size: Atoms are so small that scientific models help us understand them.
    - Model Evolution:
      - The model of the atom has evolved from J. J. Thomson's plum pudding model.
      - The current model includes a small, dense nucleus surrounded by a cloud of electrons:
        - Nucleus Composition: Contains positive protons and neutral neutrons.
        - Electron Cloud: Surrounds the nucleus, containing tiny negative electrons.
        - Neutral Atoms: Contain an equal number of protons (+) and electrons (–).

• Stability and Change:
    - Proton Count: Atoms of the same element have the same number of protons in their nucleus.
    - Isotopes:
      - Atoms of the same element can have different numbers of neutrons, leading to different masses.
      - Nuclide Notation: To represent different atoms and isotopes:
        - Format: $X^{A}<em>{Z}$         - X: Chemical symbol of the element         - A: Mass number (number of protons + neutrons)         - Z: Atomic number (number of protons)     - Example for Hydrogen:       - Hydrogen isotopes: $^{1}</em>{1}H, ext{ }^{2}<em>{1}H, ext{ }^{3}</em>{1}H$

• Stability:
    - Atoms can be stable or unstable.
    - Unstable atoms have weak forces holding protons and neutrons together, leading to decay into other elements, termed as radioisotopes.
    - Natural Radioactivity: Emission without any external energy supply.
    - Types of Nuclear Radiation:
      - Alpha Particles (α):
        - Composition: Positively charged helium nuclei (2 protons, 2 neutrons).
        - Properties: Cannot easily penetrate materials.
      - Beta Particles (β):
        - Types: Can be positive or negative, identical in size and mass to electrons.
        - Properties: Travel near the speed of light, can penetrate human skin.
      - Gamma Rays (γ):
        - Description: Bursts of energy emitted post alpha/beta emission.
        - Properties: Travel at the speed of light, very penetrating.

6.7.2 Using Radioactivity

• Half-Life:
    - Definition: The time required for half of the nuclei in a radioisotope sample to decay.

• Background Radiation:
    - Origin: Arises from natural radioactive substances and cosmic radiation.

• Applications of Radioactivity:
    - Radiometric Dating: Utilizes known half-lives of radioactive elements for dating.
      - Example: Radiocarbon dating for archaeological samples.
        - Degradation: Older samples dated via the decay of uranium to lead.
    - Nuclear Reactors:
      - Function: Uranium serves as fuel, is bombarded with neutrons, undergoing fission to produce smaller atoms and release significant energy.
      - Process: Energy is converted to steam that drives turbines for electricity generation.
      - Environmental Aspect: Low greenhouse gas emissions but produces difficult to dispose of radioactive waste.
    - Medical Applications:
      - Internal/External Radiotherapy: Radioisotopes used in cancer treatment.
        - Internal therapy: Also called brachytherapy, placing radioisotopes inside or near the tumor.
      - Diagnosis: Use of radioactive tracers for disease detection.
      - Food Preservation: Radioisotopes eliminate microbes in food.

6.7.3 Dark Side of Radiation

• Nuclear Disasters:
    - Notable events include: Chernobyl (1986) and Fukushima (2011).
    - Nuclear Weapons:
      - Use energy from nuclear reactions to deliver explosive blasts and chemical fallout, causing mass casualties.
      - Long-term impacts include diseases and genetic anomalies from exposure to fallout.

6.7.4 Key Terms

• Alpha Particles: Positively charged nuclei of helium atoms, comprising two protons and two neutrons.

• Atomic Number: The number of protons in an atom's nucleus, defining the element.

• Beta Particles: Charged particles (positive or negative) with electron-like size and mass.

• Cosmic Radiation: Naturally occurring background radiation from outer space.

• Decay: The transformation into more stable atomic forms.

• Electromagnetic Pulse: Burst of electromagnetic activity following a nuclear explosion.

• Electrons: Negatively charged subatomic particles orbiting the nucleus, much lighter than protons/neutrons.

• Element: A fundamental chemical species composed solely of one type of atom.

• Fission: Process of splitting large atomic nuclei into smaller ones, releasing energy.

• Gamma Rays: High-energy electromagnetic waves emitted during radioactive decay, massless and traveling at light speed.

• Ground Zero: The center of a nuclear explosion.

• Half-Life: Time for half the radioactive isotopes to decay into other elements.

• Radioisotope: A radioactive variant of an isotope.

• Radiocarbon Dating: Method for determining the age of fossils by measuring remaining radioactive carbon.

• Radiographic Techniques: Imaging processes using x-rays or gamma rays.

• Stable Atom: An atom whose nucleus does not undergo spontaneous change.

• Subatomic Particles: Electrons, protons, and neutrons as constituents of atoms.

• Thermal Flash: Intense heat and radiation released in a nuclear explosion's core.

6.7.5 Additional Concepts

• Nuclear Reactors: Power plants where uranium's radioactive properties are exploited for energy.

• Neutrons: Subatomic particles in the nucleus with no charge, equal mass to protons.

• Nuclear Fallout: Irradiated particulate matter descending post-explosion.

6.7.6 Resources for Learning

• eWorkbook: Study checklist (ewbk-12438)

• eWorkbook: Reflection (ewbk-12445)

• eWorkbook: Literacy builder (ewbk-12439)

• eWorkbook: Crossword (ewbk-12441)

• eWorkbook: Word search (ewbk-12443)

• Solutions: Topic 6 Solutions (sol-1139)

• Practical Investigation eLogbook: Topic 6 (elog-2313)

• Digital Document: Topic 6 Key Terms Glossary (doc-40141)

6.7 Review Questions

• Remember and Understand: Questions Q1 - Q5

• Apply and Analyze: Questions Q6 - Q10

• Evaluate and Create: Questions Q11 & Q12