Chemistry NCEA L1 AS92023 - STRUCTURE → PROPERTIES → USES

Why is copper useful for electrical wires?

Copper is metallic and has delocalised electrons that can move through the structure, giving it high electrical conductivity, so it is suitable for carrying electrical current.

Why is copper useful for electrical wiring despite being flexible?

Metallic bonding allows layers of atoms to move relative to one another without the structure breaking, making copper ductile and able to be formed into wires.

Why are metals useful for cooking pans?

Metals have strong metallic bonding and delocalised electrons, allowing them to transfer thermal energy efficiently.

Why are metals useful for structural materials?

Strong metallic bonding gives many metals strength while allowing them to be shaped without easily fracturing.

Why is aluminium useful for some structures?

Aluminium is relatively low density while still having useful strength and metallic properties, making it useful where low mass is important.

Why is lead useful for pipes?

Lead is a metallic solid that is malleable, allowing it to be shaped into pipes.

Why are ionic compounds useful as fertilisers?

Ionic compounds can dissolve in water, allowing their ions to become mobile and available in soil.

Why is salt soluble in water?

Polar water molecules attract the positive and negative ions in the ionic lattice, helping separate and surround the ions.

Why doesn't solid salt conduct electricity?

The ions are held in fixed positions in the ionic lattice and cannot move to carry charge.

Why can salt water conduct electricity?

The ions become separated and mobile in the water, allowing electrical charge to move through the solution.

Why is an ionic material unsuitable for an object that needs to bend?

Ionic lattices are brittle because shifting layers can bring similarly charged ions together, causing repulsion and fracture.

Why are ionic materials suitable for some high-temperature applications?

Strong electrostatic attractions between ions require a large amount of energy to overcome, giving them high melting points.

Why is diamond useful for cutting tools?

Diamond has a rigid three-dimensional covalent network with very strong covalent bonds, giving it extremely high hardness.

Why is diamond not suitable for electrical wiring?

Its electrons are held in covalent bonds rather than being delocalised, so it does not conduct electricity effectively.

Why is graphite useful as an electrical conductor?

Graphite has delocalised electrons that can move through its layers, allowing it to conduct electricity.

Why is graphite useful as a lubricant?

Strong covalent bonds hold each layer together, but weak attractions between layers allow the layers to slide over one another easily.

Why is graphite softer than diamond?

Graphite has weak attractions between its layers, allowing them to slide, whereas diamond has strong covalent bonds throughout a three-dimensional network.

Why are covalent networks useful at high temperatures?

Their strong covalent bonds require large amounts of energy to break, giving them high melting points.

Why are polymers useful for non-stick coatings?

Their molecular structure and surface interactions can reduce adhesion to other substances, making materials less likely to stick.

Why can polymers be used as electrical insulation?

Most polymers lack mobile charged particles or delocalised electrons, so electrical charge cannot move easily through them.

Why are polymers useful when low density is needed?

Many polymers have relatively low density compared with metals, while still being strong enough for many applications.

Why can polymer properties be changed for different uses?

Changing the polymer structure, chain arrangement, side groups or cross-linking changes the attractive forces and movement of the chains, changing physical properties.

Why does a material with stronger attractive forces generally have a higher melting point?

More energy is needed to overcome the stronger attractions holding the particles together.

Why does a material with mobile charged particles conduct electricity?

Moving charged particles can transport electrical charge through the material.

Why do delocalised electrons make metals electrically conductive?

The electrons are not restricted to one atom and can move through the metallic structure when an electric field is applied.

Why does a rigid particle arrangement often produce hardness?

Particles are strongly held in fixed positions, so the structure resists being deformed.

Why does weak attraction between particles make a substance easier to separate?

Less energy is needed to overcome the attractions, so particles can separate more easily.

How would you explain why a material is suitable for a particular use at Merit?

State the relevant physical property and explain how the material's structure or bonding produces that property, then link it to the use.

How would you reach Excellence when comparing two materials?

Compare the relevant physical properties and justify which material is more suitable by linking each property to particle arrangement and the relative strength of attractive forces.

What is a strong Excellence chain for any material question?

Type of material → particles/arrangement → bonding or attractive forces → physical property → suitability for the specific use.

If a question asks which material is best, what should you do?

Use the data provided, identify the relevant physical properties, explain them using structure and bonding, and justify why the chosen material is better suited to the use than the alternatives.

Why should you use the context in an Excellence answer?

The material is not automatically best just because it has a desirable property; you must explain why that property is important for the specific use.