Properties and Structure of Matter – Quick Revision

Classification of Substances

  • Every substance is either a pure substance or a mixture
  • Pure substance: composition is uniform; not contaminated by other substances
  • Impure substance: a mixture
  • Subtypes of pure substances: Elements, Compounds
  • Subtypes of mixtures: Homogeneous mixture, Heterogeneous mixture

Pure Substances: Elements

  • Pure substance containing only one type of atom
  • Each element has a unique set of properties
  • Listed in the periodic table with its symbol and atomic number
  • Cannot be separated into parts by physical or chemical processes
  • Examples: Oxygen, Iron, Copper, Lead, Chlorine

Pure Substances: Compounds

  • Pure substance containing two or more elements chemically bonded in fixed ratios
  • Each compound has properties distinct from its constituent elements
  • Cannot be separated by physical processes; decomposed by chemical processes
  • Examples: Water, Salt, Copper sulfate, Ethanol

Mixtures

  • NOT pure substances; contain different types of particles (elements and/or compounds)
  • Composition and properties may vary
  • Can be separated into parts by physical processes
  • Subtypes:
    • Homogeneous mixtures: uniform composition throughout (e.g., Steel, Coffee, Mouthwash, Air)
    • Heterogeneous mixtures: variable composition (e.g., Concrete, Strawberry jam, Chocolate chip cookies)

Types of Substances: Solutions, Suspensions, Colloids

  • Solutions: solute dissolved in solvent; in aqueous solutions the solvent is water
  • Suspensions: solute does not dissolve significantly; particles settle over time
  • Colloids: particles are small clusters distributed evenly; do not settle on standing

Separation of Mixtures

  • Separation method depends on the components and their properties
  • Look for differences between components (one property present in one but not the other)
  • Useful properties: particle size, boiling points, solubility/miscibility, density, magnetism, electrostatic interactions
  • All separation processes are physical changes (no new substances formed)

Separation Techniques

  • Sieving: based on particle size differences
  • Filtration: relies on particle size and solubility; can separate a solid from a liquid
  • Evaporation: uses differences in boiling points to remove a solvent
  • Distillation: separates liquids by different boiling points; distillate is collected
  • Fractional Distillation: multiple vaporisations and condensations via a fractionating column
  • Sedimentation and Decanting: based on density differences
  • Separating funnel: separates immiscible liquids based on density
  • Centrifuge: separates by density using rapid spinning

Gravimetric Analysis and Percentage Composition

  • Gravimetric analysis: determining the masses of components to find composition
  • For mixtures: ext{Percentage by mass of component} = rac{m{ ext{component}}}{m{ ext{total}}} imes 100
  • For compounds: ext{Percentage by mass of element} = rac{m{ ext{element}}}{m{ ext{compound}}} imes 100
  • Mass of a component: m{ ext{component}} = rac{ ext{percentage}}{100} imes m{ ext{total}}
  • Example (compound H$2$SO$4$):
    • Molar mass: M<em>H</em>2SO4=2(1.008)+32.07+4(16.00)=98.086 g/molM<em>{\text{H}</em>2\text{SO}_4} = 2(1.008) + 32.07 + 4(16.00) = 98.086 \text{ g/mol}
    • %H: %H=2.01698.086×100≈2.055%\% \text{H} = \frac{2.016}{98.086} \times 100 \approx 2.055\%
    • %S: %S=32.0798.086×100≈32.70%\% \text{S} = \frac{32.07}{98.086} \times 100 \approx 32.70\%
    • %O: %O=64.0098.086×100≈65.25%\% \text{O} = \frac{64.00}{98.086} \times 100 \approx 65.25\%
  • Example (mixture BaSO$4$/MgSO$4$): %BaSO$4$ ≈ 42.1%, %MgSO$4$ ≈ 57.9%

Worked Examples and Practice (key patterns)

  • Mass of component in a mixture: m{ ext{component}} = rac{ ext{percentage}}{100} imes m{ ext{total}}
  • Mass of a component in a mixture with known percentage: apply above
  • In a compound, distribute mass by element using their percentage; remaining mass is assigned to other elements
  • Example calculation pattern: identify total mass, apply percentage to find each component mass, use subtraction for remainder when needed

Mass Percent Composition of Compounds (examples)

  • Example: H$2$SO$4$ as above: final percentages for H, S, O
  • Example: For a compound with multiple elements, compute each element’s mass using its percentage and the total mass, then verify by summing to the total mass

Physical Properties and Periodic Table basics

Physical Properties of Substances

  • Definition: observable or measurable without changing the substance
  • Examples: melting point, boiling point, colour, particle size, density, solubility, hardness, electrical and thermal conductivity, viscosity, surface tension

Physical Properties of Elements

  • Elements can be classified by physical properties such as state at room temperature and metallic character
  • States of Matter at room temp (approximate): solids, liquids, gases
  • Metallic Character: metals, non-metals, metalloids

States of Matter and the Periodic Table

  • Metals: typically solid at room temperature (except mercury), shiny, good conductors, malleable and ductile
  • Non-metals: solids or gases at room temperature (except bromine); dull or non-lustrous; poor conductors; not malleable or ductile
  • Metalloids: properties between metals and non-metals

Chemical Properties of Elements

  • Chemical properties include reactivity with water, reactivity with acids, oxidation, and corrosion
  • Most chemical properties relate to an element’s reactivity, largely determined by its valency

Inference from Periodic Table

  • Elements can be inferred by position on the Periodic Table to anticipate physical and chemical properties