Overview
This lecture provides a comprehensive overview of key GCSE Chemistry topics, including states of matter, atomic structure, chemical bonding, calculations, electrolysis, periodic trends, environmental chemistry, organic compounds, polymers, and laboratory techniques.
States of Matter & Changes
- Solids: particles tightly packed, fixed positions, strong forces, low kinetic energy.
- Liquids: particles slightly apart, move freely, intermediate forces.
- Gases: particles far apart, high kinetic energy, weak forces.
- Melting = solid → liquid; Freezing = liquid → solid.
- Boiling/Evaporation = liquid → gas; Condensation = gas → liquid.
- Evaporation: highest energy particles escape first, reducing average kinetic energy.
- Diffusion: movement from high to low concentration, passive process.
Atomic Structure & Elements
- Atom: smallest particle of an element.
- Element: substance with one type of atom, found on the periodic table.
- Compound: 2+ elements chemically combined; mixture: 2+ substances physically mixed.
- Molecule: 2+ atoms bonded (same or different elements).
- Atom contains protons (+1), neutrons (0), electrons (-1); mass mostly in nucleus.
- Atomic number = protons; mass number = protons + neutrons.
- Isotopes: same protons, different neutrons.
- Ion: charged particle formed by gaining/losing electrons.
The Periodic Table & Electron Configurations
- Groups: columns, same number of outer electrons.
- Periods: rows, same number of electron shells.
- Group 0 = noble gases, full outer shell, unreactive.
- Metals: left side; non-metals: right side.
- Electronic configuration: 2 electrons in first shell, up to 8 in next.
Chemical Bonding
- Ionic bonding: metal + non-metal, transfer of electrons, oppositely charged ions attract.
- Covalent bonding: two non-metals share electrons for full outer shells.
- Example diagrams: NaCl, MgF₂, Al₂O₃ (ionic); H₂O, CH₄, CO₂, C₂H₄ (covalent).
Structures & Properties
- Giant ionic: high melting points, conduct electricity when molten/aqueous, brittle.
- Giant covalent (diamond/graphite): very high melting points, diamond does not conduct; graphite conducts.
- Simple molecular: low melting/boiling points, weak intermolecular forces.
- Giant metallic: positive ions, sea of delocalized electrons, conduct electricity/heat, malleable.
Chemical Calculations
- Relative atomic mass (Ar), formula mass (Mr).
- Moles = mass/Mr; mass = moles × Mr.
- Empirical formula: simplest ratio of atoms in a compound.
- Titration: use N = C × V (n= moles, C= concentration, V= volume).
- Avogadro’s constant: 6.02 × 10²³ = number of particles in a mole.
Electrolysis
- Electrolysis splits ionic substances using electricity; must be molten/aqueous.
- Cations (+) move to cathode (−); anions (−) move to anode (+).
- At cathode: least reactive positive ion is reduced; at anode: halide ion or OH⁻ may be oxidized.
- Products/equations depend on ions present and reactivity.
Rates of Reaction & Energetics
- Higher temperature, concentration, or surface area increases rate.
- Exothermic: releases heat (negative ΔH); endothermic: absorbs heat (positive ΔH).
- Activation energy: minimum energy to react; catalysts lower activation energy.
Chemical Equilibria
- Reversible reactions reach dynamic equilibrium in a closed system.
- Increasing temperature favors endothermic direction; increasing pressure favors side with fewer gas moles.
- Catalysts speed both forward/reverse reactions, do not change equilibrium position.
Redox & Oxidation States
- Oxidation = loss of electrons, reduction = gain (OIL RIG).
- Oxidation state rules: uncombined elements=0, ions = charge, sum in a molecule=0, group numbers predict common states.
Acids, Bases, & Salts
- Acid: donates H⁺, turns litmus red; base: accepts H⁺, turns litmus blue.
- Alkali: soluble base.
- Strong acids/bases fully dissociate, weak only partially.
- Salt formed when acid H⁺ replaced by metal or ammonium.
Organic Chemistry
- Hydrocarbons: contain only C & H; alkanes (single bonds, CnH2n+2), alkenes (double bonds, CnH2n).
- Isomers: same formula, different structures.
- Crude oil separated by fractional distillation.
- Cracking: breaks long chains into shorter, more useful ones.
- Alcohols: functional group –OH; carboxylic acids: –COOH.
- Addition polymers: formed from alkenes, no byproducts.
- Condensation polymers: polyesters (diol + dicarboxylic acid), polyamides (diamines + dicarboxylic acid), water lost.
Environmental Chemistry
- Pollutants: CO₂ (global warming), CO (toxic), methane (greenhouse), NOₓ/SO₂ (acid rain).
- Greenhouse effect: greenhouse gases absorb IR, trap heat.
- Reducing impact: plant trees, reduce fossil fuels, use renewables, catalytic converters.
Metals, Reactivity & Extraction
- Reactivity series: K, Na, Li, Ca, Mg, Al, C, Zn, Fe, H, Cu, Ag, Au (most→least reactive).
- Extraction: below carbon = reduction with carbon; above carbon = electrolysis.
- Iron extracted in blast furnace; limestone removes impurities as slag.
- Alloys: mixture of metals, harder due to disrupted structure.
Qualitative Analysis & Lab Techniques
- Gas tests: H₂ (squeaky pop), O₂ (relights glowing splint), CO₂ (limewater cloudy), Cl₂ (bleaches litmus), NH₃ (turns red litmus blue).
- Flame tests for metal ions: Li⁺ (red), Na⁺ (yellow), K⁺ (lilac), Ca²⁺ (orange-red), Cu²⁺ (blue-green).
- Precipitation tests for anions: halides with AgNO₃ (Cl⁻ white, Br⁻ cream, I⁻ yellow).
- Chromatography: separates mixtures, Rf = distance traveled by substance / solvent.
- Filtration, evaporation, distillation, and separation funnel used for various mixture separations.
Key Terms & Definitions
- Atom — Smallest unit of an element.
- Isotope — Atoms with same protons, different neutrons.
- Ion — Charged atom/molecule.
- Mole — Amount of substance containing Avogadro’s number of particles.
- Empirical formula — Simplest ratio of elements in a compound.
- Covalent bond — Shared electron pair between atoms.
- Ionic bond — Attraction between oppositely charged ions.
- Homologous series — Family of organic compounds with the same functional group.
- Oxidation — Loss of electrons.
- Reduction — Gain of electrons.
- Dynamic equilibrium — Forward and reverse reactions at equal rates in a closed system.
- Functional group — Atom/group determining a compound’s chemical properties.
Action Items / Next Steps
- Practice drawing particle diagrams and bonding diagrams.
- Memorize solubility and reactivity series rules.
- Complete empirical and titration calculations.
- Review flame test and ion precipitation test colors.
- Revise definitions and processes for each topic.
- Attempt practice questions on calculations, redox, and organic nomenclature.