AQA Chemistry (8462) 4.2.2.7–4.2.2.8 · Contrast
Metals and alloys
Pure gold bends between your fingers, and pure iron is too soft for a bridge. Mix in a few atoms of something else and the metal turns hard. How can adding a little of another element change so much?
Triple Science · Foundation tier
Start here
24-carat gold scratches. 18-carat gold lasts a lifetime.
Pure, 24-carat gold is so soft that a ring made from it dents and scratches in weeks. Many wedding rings are 18-carat: three parts gold mixed with one part of other metals such as copper and silver. They keep their shape for decades.
Commit first
Why would mixing in other metal atoms make gold harder?
In a pure metal, all the atoms are the same size, so they pack in regular layers. When a force is applied, whole layers can slide over each other and the metal bends: that is why pure metals such as gold, copper, iron and aluminium are soft. An alloy is a mixture of a metal with other elements, usually other metals. The added atoms are a different size. Mix some in and test what the layers do.
The alloy mixer
Mix in atoms. Predict. Push.
0 of 2 pushed
Pure metal
Commit first. You push the top two layers of the pure metal. What happens?
Think again · conducting
“Ionic compounds only conduct when molten, so a metal must melt before it can conduct too.”
Spot the flaw
ExplainA solid copper wire carries current every day. What is wrong with the claim?
Build the chain
Why is an alloy harder than the pure metal?
The classic 3-mark explanation. Four links in order; two are false.
4 links belong. 2 do not.
The links
Your chain · 0 of 4
Alloys as useful materials · AQA 4.10.3.2 (chemistry only)
Engineer's pick
Which material for the job?
Bronze is copper and tin. Brass is copper and zinc. Steels are iron with carbon, and sometimes other metals. Aluminium alloys are low density. Choose the material for each job.
Tap a card, then tap the box it belongs in. Tap a placed card to take it back.
Command words in this lesson
- Explain
- Different-sized atoms, distorted layers, cannot slide: say all three.
- Compare
- Pure metal and alloy side by side, in the same sentence.
- Use the data
- Describe the trend, then quote numbers from the table.
Key fact
In an alloy, atoms of different sizes distort the layers, so they cannot slide over each other easily. That makes alloys harder than pure metals.
Examiner tip
Key note · AQA 4.2.2.7–4.2.2.8 (8462)
Metals and alloys
- Metals have giant structures with strong metallic bonding, so most have high melting and boiling points.
- Pure metals are soft: the layers slide over each other easily.
- An alloy is a mixture of a metal with other elements.
- In an alloy, different-sized atoms distort the layers so they cannot slide easily: alloys are harder.
- Metals conduct electricity and heat as solids: the delocalised electrons carry charge and energy.
- Ionic compounds need to be molten or dissolved to conduct; metals do not.
Photograph this card. Tomorrow, cover it and say each line first.
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Not sure why a few extra atoms matter so much?
The mixer is a two-dimensional model with the delocalised electrons left out for clarity. Added atoms are drawn larger; in some alloys, such as steel, the added carbon atoms are smaller and sit in the gaps, which distorts the layers in the same way. Recalling named alloys and their uses is separate-science content, taught only on Triple routes; elsewhere an alloy's make-up is given in the question.