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1 Atomic Structure and Properties 2 Compound Structure and Properties 3 Properties of Substances and Mixtures 4 Chemical Reactions 5 Kinetics 6 Thermochemistry 7 Equilibrium 8 Acids and Bases 9 Thermodynamics and Electrochemistry

4 Chemical Reactions

4.1 Introduction for Reactions 4.2 Net Ionic Equations 4.3 Representations of Reactions 4.4 Physical and Chemical Changes 4.5 Stoichiometry 4.6 Introduction to Titration 4.7 Types of Chemical Reactions 4.8 Introduction to Acid-Base Reactions 4.9 Oxidation-Reduction (Redox) Reactions

Particulate Representations of Equations

Learning Objective 4.3.A Represent a given chemical reaction or physical process with a consistent particulate model.

Quick Notes

  • Particulate models use dots, circles, or shapes to represent atoms, ions, or molecules at the particle level.
  • These models help visualize how atoms rearrange during chemical reactions or physical processes.
  • A consistent particulate model should:
    • Accurately reflect the chemical formulas of substances.
    • Show correct ratios of reactants and products, based on a balanced chemical equation.
    • Use distinct symbols or shading to represent different elements or ions.
  • Useful for showing:
    • Conservation of mass (number of atoms)
    • Conservation of charge (especially in ionic reactions)
    • Phase (solid, liquid, gas, aqueous)

Full Notes

Particulate representations (also called particulate-level diagrams or molecular-level models) illustrate chemical and physical changes by showing individual particles – atoms, molecules, and ions – interacting and rearranging.

These visual models are especially helpful for understanding:

What Makes a Good Particulate Representation?

Example: Precipitation Reaction

Balanced equation: AgNO₃(aq) + NaCl(aq) → AgCl(s) + NaNO₃(aq)

Particulate representation of silver nitrate and sodium chloride reaction forming silver chloride precipitate and sodium nitrate in solution.

Before: silver ions (Ag⁺) and nitrate ions (NO₃⁻) floating separately in solution with sodium (Na⁺) and chloride ions (Cl⁻).
After: silver ions and chloride ions combine to form solid AgCl (clustered together); Na⁺ and NO₃⁻ remain free in solution (spectator ions).

Net ionic equation: Ag⁺(aq) + Cl⁻(aq) → AgCl(s)

The particulate model shows:

Physical Changes Can Also Be Represented

Particles in solid are shown tightly packed in a fixed structure.
In liquid, particles are still close but move freely — not in fixed positions.

Particulate model showing solid water (ice) particles arranged in a fixed structure changing to liquid water particles moving freely.

Example:H2O(s) → H2O(l)

Note: This is a simplification of the arrangement of molecules in solid ice — they are actually less dense than molecules in liquid water (see water and ice bonding).

Summary