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Materials chemistry studies substances used to make useful objects, including plastics, metals, ceramics, glass, fibres and composites.
| Material Type | Examples | Useful Properties |
|---|---|---|
| Polymers/plastics | Polyethene, PVC, nylon | Light, mouldable, waterproof, cheap. |
| Metals | Iron, aluminium, copper | Strong, conductive, malleable. |
| Ceramics | Brick, porcelain, glass | Hard, heat-resistant, often brittle. |
| Composites | Fibreglass, reinforced concrete | Combine properties of different materials. |
A polymer is a large molecule made by joining many small molecules called monomers.
| Term | Meaning | Example |
|---|---|---|
| Monomer | Small molecule that can join to others. | Ethene, C₂H₄ |
| Polymer | Very large molecule made from many monomers. | Polyethene |
| Polymerisation | Reaction where monomers join to form a polymer. | Ethene → polyethene |
Addition polymerisation happens when many alkene monomers join together. The carbon-carbon double bond opens and forms single bonds in a long chain.
The polymer formed from ethene is polyethene.
| Monomer | Polymer | Uses |
|---|---|---|
| Ethene | Polyethene | Plastic bags, bottles, packaging. |
| Propene | Polypropene | Ropes, crates, food containers. |
| Chloroethene | PVC | Pipes, window frames, cable insulation. |
| Type | Structure | Heating Behaviour | Example Uses |
|---|---|---|---|
| Thermoplastic | Polymer chains with weak forces between chains. | Softens when heated and can be remoulded. | Packaging, bottles, bags. |
| Thermosetting plastic | Polymer chains joined by strong cross-links. | Does not soften easily; cannot be remoulded. | Electrical plugs, saucepan handles, heat-resistant items. |
Plastic recycling reduces waste and saves raw materials, but it can be difficult because different plastics have different properties.
| Benefit of Recycling | Challenge |
|---|---|
| Reduces landfill waste. | Plastics must be sorted by type. |
| Saves crude oil/raw materials. | Food contamination can reduce quality. |
| Uses less energy than making new plastic in some cases. | Some plastics degrade after repeated recycling. |
| Reduces environmental pollution. | Collection and processing can be expensive. |
Biodegradable plastics are designed to break down more easily through the action of microorganisms under suitable conditions.
| Advantage | Limitation |
|---|---|
| Can reduce long-term plastic waste. | May need specific composting conditions. |
| Useful for packaging and bags. | May not break down quickly in landfill or the ocean. |
| Can be made from renewable materials. | Can still cause litter if disposed of incorrectly. |
A crystal has particles arranged in a regular repeating pattern. Different crystal structures give different properties.
| Crystal Type | Particles | Example | Key Property |
|---|---|---|---|
| Ionic crystal | Positive and negative ions | Sodium chloride | High melting point; conducts when molten/dissolved. |
| Molecular crystal | Molecules | Iodine, ice | Lower melting point due to weak intermolecular forces. |
| Giant covalent crystal | Atoms joined by covalent bonds | Diamond, graphite, silicon dioxide | Very high melting point. |
| Metallic crystal | Positive metal ions and delocalised electrons | Copper, iron, aluminium | Conducts electricity and is malleable. |
| Property | Diamond | Graphite |
|---|---|---|
| Structure | Each carbon bonded to four others. | Each carbon bonded to three others in layers. |
| Hardness | Very hard. | Soft/slippery because layers slide. |
| Electrical conductivity | Does not conduct. | Conducts due to delocalised electrons. |
| Uses | Cutting tools, jewellery. | Pencils, lubricants, electrodes. |
Use for: Understanding molecules and repeating units.
Use for: Linking structure and properties in chemistry contexts.
Q1. Define polymer and monomer. [4 marks]
Q2. Explain addition polymerisation using ethene as an example. [3 marks]
Q3. Compare thermoplastics and thermosetting plastics. [4 marks]
Q4. Give two advantages and two difficulties of recycling plastics. [4 marks]
Q5. Explain why graphite conducts electricity but diamond does not. [4 marks]
Q6. Name two types of crystal structure and give one example of each. [4 marks]
1. A polymer is made from many: A. neutrons B. monomers C. metals only D. ions only
Answer: B. Polymers are made from repeating monomers.
2. Addition polymerisation usually involves: A. alkenes B. noble gases C. salts only D. water only
Answer: A. Alkenes have C=C bonds that can open and join.
3. Thermoplastics can be: A. remoulded B. never heated C. only metals D. ozone gases
Answer: A. Thermoplastics soften when heated and can be remoulded.
4. Graphite conducts because it has: A. delocalised electrons B. no bonds C. free oxygen D. water molecules
Answer: A. Delocalised electrons carry charge.
To match the full Ordinary Level syllabus, students should clearly recognise the main crystal types and know that X-rays can be used to investigate crystal structure.
| Crystal Type | Particles Present | Forces / Bonds | Example | Key Property |
|---|---|---|---|---|
| Ionic crystal | Positive and negative ions | Strong electrostatic attraction | Sodium chloride | High melting point; conducts when molten or in solution |
| Molecular crystal | Molecules | Weak intermolecular forces | Iodine / ice | Lower melting point; usually poor conductor |
| Metallic crystal | Positive metal ions and delocalised electrons | Metallic bonding | Copper / aluminium | Good conductor; malleable |
| Giant covalent crystal | Atoms joined in a network | Covalent bonds | Diamond / graphite / silicon dioxide | Very high melting point |
X-ray crystallography is used to investigate how particles are arranged inside crystals. X-rays are diffracted by the regularly spaced layers of particles, and the pattern helps scientists work out the crystal structure.
Bragg helped explain X-ray diffraction from crystals, and Dorothy Hodgkin used X-ray methods to study important molecular structures. Buckminsterfullerene is another carbon allotrope with a cage-like structure.
The syllabus expects named examples of common addition polymers and their uses.
| Monomer | Polymer | Typical Use |
|---|---|---|
| Ethene | Poly(ethene) | Bags, films, bottles |
| Ethene under controlled conditions | Low-density polyethene (LDPE) | Flexible packaging, films |
| Ethene under different conditions | High-density polyethene (HDPE) | Bottles, containers, stronger plastic items |
| Chloroethene | Poly(chloroethene) / PVC | Pipes, cable insulation, frames |
| Phenylethene | Poly(phenylethene) / polystyrene | Packaging, cups, insulation |
The materials option also expects a short treatment of metals, alloys, and the effect of carbon in steel.
| Feature | Metals | Non-metals |
|---|---|---|
| Conductivity | Usually good conductors of heat and electricity | Usually poor conductors |
| Malleability | Malleable and ductile | Brittle if solid |
| Appearance | Usually shiny | Often dull |
An alloy is a mixture of a metal with one or more other elements. Alloys are often harder or more useful than pure metals.
| Alloy | Main Composition | Why Useful |
|---|---|---|
| Brass | Copper + zinc | Harder than copper; corrosion resistant |
| Bronze | Copper + tin | Hard and durable |
| Steel | Iron + carbon | Stronger and harder than pure iron |
Adding small amounts of carbon to iron makes steel harder. More carbon usually gives greater hardness, but too much can make steel more brittle.