Chemistry IGCSE Notes

The Particulate Nature of Matter

  • Kinetic Particle Theory:
    • Heating solids increases particle vibration and expansion.
    • Melting occurs when particles overcome strong forces, allowing them to slide.
    • Liquids: particles move but remain close.
    • Boiling: particles gain enough energy to escape and move rapidly.
    • Vapor: rapid, random motion due to collisions.
  • States of Matter:
    • Solid: Strong forces, fixed pattern (lattice), fixed volume/shape.
    • Liquid: Weaker forces, no fixed pattern, takes container shape, particles slide.
    • Gas: Almost no intermolecular forces, particles move quickly and collide.
  • Phase Changes:
    • Melting, Boiling, Sublimation: Endothermic (heat gained).
    • Condensing, Freezing, Reverse sublimation: Exothermic (heat lost).
  • Diffusion:
    • Spreading of a substance from high to low concentration due to continuous random motion.
    • Factors: Temperature (↑ increases rate), Density (lower density gas ↑ rate).

Experimental Techniques

  • Measurement Apparatus:
    • Time: Stopwatch or Clock
    • Temperature: Thermometer (liquid in glass, thermistor or thermocouple)
    • Mass: Balance
    • Volume: Beaker, Burette, Pippette, Measuring Cylinder, Gas Syringe
  • Paper Chromatography:
    • Separates substances based on solubility differences.
    • Stationary phase: Material on which separation occurs.
    • Mobile phase: Mixture dissolved in a solvent.
    • R_f Value = \frac{Distance\ moved\ by\ solute}{Distance\ moved\ by\ solvent}
    • Locating agents are used to visualize colorless substances.
  • Purity Assessment:
    • Pure substances have sharp m.p./b.p.
    • Impurities lower m.p. and raise b.p.
  • Separation Techniques:
    • Filtration: separates insoluble residue from filtrate.
    • Crystallization: evaporation, cooling, and filtering of crystals,
    • Simple Distillation: separates liquid from impurities, based on boiling point.
    • Fractional Distillation: separates liquids with different boiling points.
    • Separating Mixture of Two solids: dissolving one in appropriate solvent, using magnet if one solid magnetic.
  • Solvents:
    • Water: Some salts, sugar
    • White spirit: Gloss paint
    • Propanone: Grease, nail polish
    • Ethanol: Glues, printing inks, scented substances
  • Method Selection:
    • Filtration: Solid from liquid
    • Evaporation/Crystallization: Solid from solution
    • Simple Distillation: Solvent from solution
    • Fractional Distillation: Liquids from each other
    • Chromatography: Different substances from a solution

Atoms, Elements, and Compounds

  • Atomic Structure:
    • Particle: Proton (+1 charge, 1 mass), Neutron (0 charge, 1 mass), Electron (-1 charge, 1/1837 mass)
    • Proton number: number of protons
    • Nucleon number: number of protons + neutrons
    • Isotopes: same element, different neutron number.
  • Electron Arrangement:
    • Electrons arranged in shells (2, 8, 8, 18).
    • Atoms react to achieve full outer shells.
    • Noble gases are inert due to full outer shells.
  • Bonding:
    • Element: cannot be split chemically.
    • Mixture: not chemically combined.
    • Compound: chemically combined elements
  • Ions and Ionic Bonds:
    • Electron transfer forms ions; metals lose electrons (cations), non-metals gain (anions).
    • Ionic bond: electrostatic attraction between cations and anions.
  • Molecules and Covalent Bonds:
    • Atoms share electrons.
    • Single, double, and triple bonds (2, 4, 6 shared 𝑒̅s).
  • Macromolecules:
    • Diamond: Four bonds, high m.p., doesn’t conduct, hard.
    • Graphite: Three bonds, flat sheets, soft, conducts electricity.
    • Silicon Dioxide: High m.p., hard.
  • Metallic Bonding
    • Positive ions held together by electrons.

Stoichiometry

  • Balancing Equations: Equal atoms & charges on both sides using state symbols (s, l, g, aq).
  • Valency Table:
    • Nitrate NO3^{-}, Hydroxide OH^{-}, Acetate CH3COO^{-}: Valency 1
    • Carbonate CO3^{2-}, Sulphate SO4^{2-}, Silicate SiO_3^{2-}: Valency 2
    • Phosphate PO_4^{3-}: Valency 3
  • Naming Conventions:
    • -ide: two elements
    • -ate: contains oxygen
  • Masses:
    • A_r: Relative atomic mass (relative to Carbon-12)
    • Mr: Relative molecular mass (sum of Ar of atoms)
  • The Mole Concept:
    • Mole = Ar or Mr in grams. Equal to Avogadro’s number (6.02 × 10^{23}).
  • Calculations:
    • Number \ of \ Moles = \frac{mass}{molar \ mass}
    • Volume = No. \ of \ Moles × 24dm^3
    • Concentration = \frac{no. \ of \ moles}{volume}
  • Formulae:
    • Molecular: actual number of atoms.
    • Empirical: simplest ratio of atoms.
  • Percentages:
    • Percentage \ purity = \frac{mass \ of \ product \ (pure)}{mass \ of \ compound \ (impure)} × 100
    • Percentage \ yield = \frac{actual \ mass \ obtained}{calculated \ mass} × 100

Electricity and Chemistry

  • Electrolysis: decomposition by electric current.
    • Electrolyte: solution/molten salt with mobile ions
    • Electrodes: rods for current entry.
  • Principle:
    • Molten electrolyte: Metal at cathode, Non-metal at anode
    • Aqueous electrolyte: depends on reactivity
  • Electroplating: coating metal with another using electrolysis.
  • Uses:
    • Aluminum: electricity cables (light, non-corrosive).
    • Copper: electrical wires (good conductor).
    • Plastics/Ceramics: insulators.
  • Refining Metals: purifying impure metals with electrolysis
  • Basics
    • Reduction at cathode, oxidation at anode.
  • Extraction of Aluminium
    • Aluminium oxide dissolved in molten cryolite (lower m.p.).
    • Aluminium produced at cathode, oxygen at anode
  • Electrolysis of Brine
    • Brine = concentrated NaCl solution
    • Chlorine gas evolved at anode, hydrogen gas and aqueous sodium hydroxide at cathode

Chemical Energetics

  • Reactions:
    • Exothermic: releases heat.
    • Endothermic: absorbs heat.
    • Bond breaking: endothermic, bond making: exothermic.
    • \Delta H = Bond \ Breaking + Bond \ Forming
  • Energy Production:
    • Fuels produce energy when burned.
  • Hydrogen:
    • ADVANTAGES: A lot of energy, abundant, less pollutant, renewable
    • DISADVANTAGES: Difficult to transport, dangerous mix with air - explosive
  • Simple Cells:
    • Two metals of different reactivity connected by an external circuit and an electrolyte
  • Radioactive Isotopes:
    • Uranium-235 in nuclear power stations generates heat
    • ADVANTAGES: lots of energy
    • DISADVANTAGE: radioactive waste

Chemical Reactions

  • Collision Theory:
    • Collisions needed, successful collisions need activation energy.
  • Rates of Reaction:
    • (mol/dm3)/s
  • Factors Affecting Rate:
    • Concentration: ↑ Increases collision rate.
    • Temperature: ↑ Increases kinetic energy/successful collisions
    • Particle Size: ↓ Increases surface area.
    • Pressure (gases): ↑ Increases collision rate.
  • Catalyst:
    • Speeds up reaction, remains unchanged.
    • Provides alternative pathway with lower activation energy.
    • Enzymes: biological catalysts, optimum temperature/pH.
  • Measuring Rates:
    • Gas evolved, mass loss, color change.
  • Photochemical Reactions:
    • Light initiates silver bromide breakdown in film.
  • Reversible Reactions:
    • Reactants form products, products reform reactants.
    • Dynamic equilibrium: forward rate = reverse rate.
  • Equilibrium:
    • Le Châtelier’s Principle: system opposes change.
    • Temperature: Lowered moves to exothermic direction. Raised moves to endothermic direction.
    • Pressure: Raised moves to fewer gas molecules. Lowered moves to more gas molecules.
    • Concentration: Altered to oppose change
  • Redox:
    • Oxidation: loss of electrons; reduction: gain of electrons.
    • OIL RIG
    • Oxidizing agents are reducing and reducing agents are oxidized

Acids, Bases, and Salts

  • Acids:
    • Produce H^+ ions in water, proton donors.
  • Bases:
    • Neutralize acids, proton acceptors.
  • Neutral: pH 7.
  • Indicators:
    • Phenolphthalein, Methyl orange, Methyl red, Red litmus, Blue litmus.
  • Types of Oxides:
    • Metal oxides: basic.
    • Non-metal oxides: acidic.
    • Aluminum, zinc, lead: amphoteric.
    • Water, carbon monoxide: neutral.
  • Salts:
    • Formed when replaceable hydrogen ions of an acid are replaced by metal ions or the ammonium ion
    • Preparation: from metal, insoluble base, or alkali.
  • Tests:
    • Cations, anions, gases.

The Periodic Table

  • Arrangement: increasing atomic number.
  • Organization: rows (periods), columns (groups).
  • Metals: left; non-metals: right.
  • Trends:
    • Metals: reactivity increases down a group.
    • Non-metals: reactivity decreases down a group.

Metals

  • Properties:
    • Physical: high density, shiny, malleable.
    • Chemical: form basic oxides, positive ions.
  • Alloys:
    • Improved qualities over pure metals.
  • Reactivity Series:
    • Metals compete for oxygen or anions.
  • Extraction of Metals:
    • Electrolysis, reduction with carbon
  • Uses:
    • Aluminum, Zinc, Copper
    • Air and Water
  • Tests for water, purification, and use

Organic Chemistry

  • Homologous Series:
    • Characteristics of hydrocarbons.
  • Fuels:
    • Coal, natural gas, petroleum.
  • Uses of Petroleum Fractions:
    • Names and Uses, Alkane, Alkene, alcohol and Carboxylic acid
  • Name of Compounds:
    • Ending of compounds
  • Addition Polymerisation:
    • The addition and formation of polymers
  • Sources:
    • Found as an element, underground and rims of volcanoes
    • Sulfur compounds found in fossil fuels