Properties and Uses of Metals
FoundationMetals are shiny, conduct electricity and heat, and are malleable. Different metals suit different jobs: copper conducts well (electrical wires), aluminium is light (window frames), iron is strong (bridges). Alloys (steel, brass) improve on pure metals.
- Metals: shiny, conductive, malleable, sonorous
- Properties decide uses (copper wires, aluminium frames, steel bridges)
- Alloys = metal + other elements for better properties
§Text Passage
1Metals are everywhere in daily life: iron gates, aluminium windows, copper wires and stainless-steel kitchenware are all made of them. Metals share several general properties: a metallic shine, electrical conduction, thermal conduction, malleability — they can be hammered into sheets or drawn into wires without cracking — and a ringing sound when struck. Nearly all are solid at room temperature, mercury being the only liquid exception.
2Different metals excel at different jobs, and choosing a material means matching properties to the need: copper conducts electricity superbly, so it makes wiring; aluminium is light, conducts heat well and resists corrosion, suiting aircraft parts and window frames; steel is hard and strong, serving in bridges and reinforcing bars. Density and melting point differ widely too: aluminium's density is about 2.7 g per cubic centimetre, a light metal, while tungsten melts above 3400°C and serves as light-bulb filaments.
3Pure metals are not always fit for the job. Pure iron is too soft, and only by adding carbon to make steel does it become hard and strong; pure aluminium must be turned into alloy before it can form aircraft wings; pure gold is likewise soft, so jewellery mixes in copper or silver for hardness. An alloy is made by mixing one metal with other elements: the added atoms make it hard for the neat layers of metal atoms to slide over one another, so the material becomes harder and stronger and stands up to daily wear.
4Another great advantage of metals is that they can be recycled. Mining and extracting metals consumes vast amounts of energy and damages the environment; sorting used metal for recycling saves resources on a large scale — re-melting aluminium takes only about 5% of the energy of extracting it from ore. Metals keep their properties after re-melting and can be recycled again and again, making them sustainable materials, and the habit of sorting metal waste is a practical way to lighten the load on the environment.
1Summary 重點摘要
Metals are shiny, conduct electricity and heat, and are malleable. Different metals suit different jobs: copper conducts well (electrical wires), aluminium is light (window frames), iron is strong (bridges). Alloys (steel, brass) improve on pure metals.
2Vocabulary cards Vocabulary
Can be hammered or stretched without cracking — gold can be beaten into leaf.
A material that carries electricity or heat — metals conduct well.
A mixture of a metal with other elements, e.g. steel (iron + carbon), brass (copper + zinc).
Rings when struck — like bells and gongs.
The ability of a metal surface to reflect light, especially when polished.
Can be drawn into wires without breaking — copper is drawn into cables.
How well a material carries current — copper excels, so it makes wires.
How well a material carries heat — used in pans and pots.
An alloy of iron with carbon — hard and strong, used for bridges and buildings.
3Step by step Steps
- Six general propertiesThe general properties of metals are: a metallic shine, electrical conduction, thermal conduction, malleability, a ringing sound when struck, and — mostly — being solid at room temperature, mercury being the only liquid exception. Sodium and potassium are metals yet soft enough to slice with a knife, showing that individual metals still vary around the shared pattern. These general properties arise from the free electrons moving inside metals, which also explain why metals conduct both electricity and heat so well.
- Property and use matchingChoosing a material means matching its properties to the job: copper conducts electricity superbly, so it makes wiring; aluminium conducts heat well and is light, suiting pans and aircraft; steel is hard and strong, serving in bridges and reinforcing bars. Write 'property, reason and use' — all three parts, supported by concrete examples; that structure is the standard way these questions earn marks, so check your answer against each item as you practise.
- Pure isn't always bestPure metals are not always fit for the job: pure iron is too soft — carbon is added to make the hard, strong steel we need; pure aluminium must be turned into alloy before it can form wings and window frames; pure gold is likewise soft, so jewellery mixes in copper or silver for hardness. Everyday goods therefore mostly use alloys rather than pure metals: the atomic layers in an alloy cannot slide over one another easily, so the material becomes harder and stronger and stands up to daily wear.
- Why alloys are strongerAn alloy is made by mixing one metal with other elements. The added atoms differ in size from the original ones, so the neat layers of metal atoms can no longer slide over each other easily, and the material becomes harder and stronger — steel is iron mixed with carbon, and brass is copper mixed with zinc. This 'hindered sliding' idea is the heart of understanding alloys, and it explains why alloys, rather than pure metals, are the workhorse materials of daily life.
- Density and melting point differMetals differ hugely in density and melting point: aluminium's density is about 2.7 g per cubic centimetre — a light metal ideal for aircraft and bicycle frames; iron's is about 7.9; tungsten melts above 3400°C and serves as light-bulb filaments; mercury melts at about -39°C, staying liquid at room temperature inside thermometers. When choosing a material, density and melting point matter just as much as strength and conductivity.
- Metals and recyclingMining and extracting metals consumes vast amounts of energy and damages the natural environment; sorting used metal for recycling saves resources on a huge scale — re-melting aluminium takes only about 5% of the energy of extracting it from ore. Metals keep their properties after re-melting and can be recycled again and again, making them sustainable materials; making a habit of sorting metal waste is also a practical way for each of us to lighten the load on the environment.
4Diagrams Diagrams
5Worked example Example
Why are wires made of copper, not iron? Why are planes built with aluminium alloy, not steel?
- Wires: need good conduction + resist corrosion — copper conducts better than iron and oxidises less
- Planes: need light + strong — steel is too heavy; aluminium alloy is light yet strong
- Extension: pure gold is too soft for jewellery — it is alloyed with copper or silver for hardness
- Principle: match properties to the job
- Answer: Copper conducts far better than iron and resists oxidation, so wires are copper; steel is hard but dense and heavy, while aluminium alloy is light yet strong enough, so aircraft use it. The rule is to match properties to the job, balancing weight, cost and durability. In your answer, give property, reason and use for each choice. Add alloy examples such as steel, brass and stainless steel.
6Common mistakes Mistakes
7Quick check Quick check
Q1Name two general properties of metals and a matching use.
Q2Steel is an alloy of what, with which element added?
Q3Why isn't pure iron used directly for tools?
Q4Which metal is liquid at room temperature, and what is it used for?
Q5Why is recycling aluminium greener than extracting new aluminium from ore?
8Recap Recap
- Metals: shiny, conductive, malleable, sonorous
- Properties decide uses (copper wires, aluminium frames, steel bridges)
- Alloys = metal + other elements for better properties
- Most metals are solid at room temperature — mercury is the liquid exception
- Alloys are harder: added atoms stop the metal's layers sliding