Essential Chemistry Principles and Atomic Theory

Posted on Jan 1, 2026 in Chemistry

1. Mathematics and Measurement in Chemistry

  • Chemistry utilizes mathematics for measuring, calculating, and comparing data.
  • It relies on SI Units (grams, liters, meters, Kelvin, etc.).
  • Unit conversions are common (e.g., grams to kilograms).
  • Accuracy and precision are critical in all experimental procedures.

Example: Measuring 25.0 mL of water provides precise data.

2. The Scientific Method and Data Analysis

  • Steps: Ask a question → Form a hypothesis → Experiment → Collect data → Analyze → Conclude.
  • Variables:
    • Independent: The factor you change.
    • Dependent: The factor you measure.
    • Controlled: Factors that remain constant.
  • Data illustrates relationships between variables.

Example: Temperature affects the rate at which sugar dissolves in water.

3. States and Classification of Matter

  • States of Matter:
    • Solid: Definite shape and volume.
    • Liquid: Definite volume; takes the shape of its container.
    • Gas: No fixed shape or volume.
    • Plasma: High-energy ionized gas (found in stars).
  • Classification:
    • Pure Substances: Elements and compounds.
    • Mixtures: Substances that can be separated physically.

4. Physical vs. Chemical Properties and Changes

  • Physical Property: Observed without changing the substance (e.g., color, melting point).
  • Chemical Property: Describes how a substance reacts (e.g., flammability, rusting).
  • Physical Change: The substance remains the same (e.g., melting ice).
  • Chemical Change: A new substance is formed (e.g., burning wood).

5. The Historical Evolution of Atomic Theory

  • Dalton: Atoms are solid spheres.
  • Thomson: Discovered electrons (the “plum pudding” model).
  • Rutherford: Discovered the nucleus via the gold foil experiment.
  • Bohr: Electrons move in specific energy levels.
  • Modern Model: Electrons exist in orbitals around the nucleus.

6. Organization of the Periodic Table

  • Organized by atomic number (the number of protons).
  • Groups/Families (columns): Share the same number of valence electrons and similar properties.
  • Periods (rows): Demonstrate patterns in reactivity and atomic size.
  • Elements are categorized as metals, nonmetals, or metalloids based on their properties.

Example: Group 1 (alkali metals) are highly reactive.

7. Electron Configuration and Valence Electrons

  • Electron Configuration: Describes the distribution of electrons in an atom.
  • Valence Electrons: Outer shell electrons that participate in chemical bonding.
  • These are identified using the periodic table (refer to the group number).

Example: Oxygen has 6 valence electrons and can form 2 chemical bonds.

8. Chemical Bonds and Molecular Formulas

  • Ionic Bond: Electrons are transferred (metal + nonmetal).
  • Covalent Bond: Electrons are shared (nonmetal + nonmetal).
  • Chemical Formulas: Indicate which elements and how many atoms are in a compound.
    • Example: H₂O contains 2 hydrogen atoms and 1 oxygen atom.

Tip: Ionic involves transfer; covalent involves sharing.

9. Intermolecular Forces and Molecular Attraction

  • Hydrogen Bonds: Strong attractions (e.g., in water).
  • Dipole-Dipole Forces: Occur between polar molecules.
  • Dispersion Forces: Weak forces present between all molecules.
  • These forces affect melting points, boiling points, and solubility.

10. The Law of Conservation of Mass

  • Mass is neither created nor destroyed during a chemical reaction.
  • The total mass of reactants equals the total mass of products.
  • This principle is used to balance chemical equations.

Example: H₂ + O₂ → H₂O must be balanced as 2H₂ + O₂ → 2H₂O.

11. Primary Types of Chemical Reactions

  1. Synthesis: A + B → AB
  2. Decomposition: AB → A + B
  3. Single Replacement: A + BC → AC + B
  4. Double Replacement: AB + CD → AD + CB
  5. Combustion: Hydrocarbon + O₂ → CO₂ + H₂O
  6. Redox: Involves the transfer of electrons.

12. Nuclear Reactions and Fundamental Forces

  • Nuclear Reactions: Involve changes in the atom’s nucleus.
    • Fission: The nucleus splits (utilized in nuclear power).
    • Fusion: Nuclei combine (occurs in stars).
  • These reactions release significantly more energy than standard chemical reactions.