Overview
This lecture covers key concepts for Edexcel GCSE Chemistry Paper 2, including the periodic table, chemical reactions, hydrocarbons, atmosphere, chemical tests, polymers, and nanoparticles, all at a Grade 9 standard.
The Periodic Table
- Groups are vertical columns; periods are horizontal rows.
- Elements in a group have the same number of outer shell electrons.
- Elements in a period have the same number of electron shells.
- Group 1 (alkali metals): Reactivity increases down the group, react with oxygen, chlorine, and water.
- Group 7 (halogens): Reactivity decreases down the group, form diatomic molecules, and react with metals and hydrogen.
- Group 0 (noble gases): Unreactive, full outer electron shell, boiling points increase down the group.
Rates of Reaction
- Rate = change in reactant or product quantity / time.
- Common units: g/s, cm³/s.
- Measured via change in mass or gas volume.
- Factors affecting rate: temperature, pressure, concentration, surface area, and catalysts.
- Collision theory: reactions occur when particles collide with enough energy (activation energy).
- Catalysts lower activation energy.
Energetics & Reaction Profiles
- Exothermic: energy released, temperature increases (e.g., combustion, neutralization).
- Endothermic: energy absorbed, temperature decreases (e.g., thermal decomposition).
- Activation energy: minimum energy needed for reaction.
- Energy change = bonds broken (input) – bonds made (output).
Crude Oil, Hydrocarbons & Atmospheric Pollution
- Crude oil: mixture of hydrocarbons separated by fractional distillation.
- Hydrocarbons are molecules with only C and H atoms (alkanes: CnH2n+2, alkenes: CnH2n).
- As hydrocarbon chain length increases: higher boiling point, viscosity; lower flammability.
- Complete combustion: produces CO₂ and water; incomplete combustion: CO, soot.
- Pollutants: CO (toxic), SO₂ (acid rain), NOx (smog), particulates (global dimming).
- Hydrogen fuel: produces only water but has production/storage drawbacks.
Earth's Atmosphere & Greenhouse Gases
- Present atmosphere: ~80% N₂, 20% O₂, small CO₂, noble gases.
- Early atmosphere: mostly CO₂, little/no O₂.
- Photosynthesis increased O₂ and reduced CO₂.
- Greenhouse gases: CO₂, methane, water vapor—trap infrared, causing warming.
- Human activities increase greenhouse gases (e.g., burning fuels, farming).
- Effects: global warming, droughts, sea level rise.
Chemical Analysis & Tests
- Flame tests identify metal ions (Li⁺: crimson, Na⁺: yellow, K⁺: lilac, Ca²⁺: orange-red, Cu²⁺: green).
- Sodium hydroxide test forms precipitates with specific metal ions.
- Ammonium ions: produce ammonia gas that turns damp red litmus blue when heated with NaOH.
- Carbonates: fizz with acid, turn limewater cloudy (CO₂).
- Halides: form precipitates with silver nitrate (Cl⁻: white, Br⁻: cream, I⁻: yellow).
- Sulfates: form white ppt with barium chloride.
- Instrumental methods (e.g., flame photometry) are accurate, sensitive, rapid.
Organic Chemistry: Alkanes, Alkenes, Alcohols, Carboxylic Acids, and Polymers
- Alkanes: saturated hydrocarbons, general formula CnH2n+2.
- Alkenes: unsaturated hydrocarbons with C=C, formula CnH2n, react with bromine water (decolorizes).
- Cracking converts long alkanes to shorter alkanes and alkenes.
- Alcohols: contain -OH, end in 'anol', soluble, react with Na (bubbles), oxidized to carboxylic acids.
- Carboxylic acids: contain -COOH, weak acids, react with metals, bases, carbonates, and alcohols (form esters).
- Addition polymerization: monomers form long chains (e.g., polyethene).
- Condensation polymers form with loss of small molecules (e.g., water).
Nanoparticles & Ceramics
- Nanoparticles: 1–100 nm, large surface area to volume, used in medicine, electronics, cosmetics, catalysts.
- Risks: can enter cells, catalyze harmful reactions.
- Glass ceramics (soda-lime, borosilicate), clay ceramics (pottery, bricks): properties and uses.
Key Terms & Definitions
- Group (Periodic Table) — vertical column of elements with similar properties.
- Period — horizontal row of elements.
- Activation energy — minimum energy required for particles to react.
- Homologous series — family of organic compounds with similar properties and the same general formula.
- Cracking — breaking long-chain hydrocarbons into shorter, useful ones.
- Greenhouse gas — gas that absorbs and emits infrared radiation.
- Monomer — small molecule that forms polymers.
- Polymer — large molecule made from repeating monomers.
- Nanoparticle — particle 1–100 nm in size.
Action Items / Next Steps
- Review periodic table groups, especially 1, 7, and 0.
- Memorize chemical tests and flame colors for metal ions.
- Practice calculations for rates of reaction and energy changes.
- Understand and practice drawing and naming organic molecules.
- Complete homework or predicted papers as provided by your teacher.