Alloys — Extraction and Uses of Metals | IGCSE Chemistry

Exam Frequency Analysis

Past paper frequency (2018 to 2024)

This topic accounts for approximately 6% of your exam marks.

stable

Low

Stable6%

Blast furnace chemistry and electrolytic extraction of aluminium regularly examined.

What an alloy is

An alloy is a mixture of a metal with one or more other elements, usually another metal or a non-metal such as carbon
Examples already encountered:
- Steel: iron + carbon (see section 3)
- Brass: about 70% copper + 30% zinc — used for fittings, decorative work and musical instruments
- Bronze: copper + tin — used for statues, bells and bearings

Why alloys are harder than the pure metal

Pure metals deform easily because layers of identical-size atoms slide cleanly over one another (this was the malleability argument in topic 08)
In an alloy, the added element has atoms of a different size, which disrupts the regular layered packing
The disrupted layers can no longer slide smoothly, so the alloy is harder and more rigid
Many alloys are also chosen because they resist corrosion (stainless steel, bronze) or tolerate higher temperatures (nichrome heating elements)
The detailed structural picture sits in topic 08 Metallic Bonding, section 3

Exam tip

Explain why an alloy is harder (less malleable) than the pure metal

What comes up: a 2–3-mark question asking you to use a diagram of particle arrangement to explain why an alloy is harder or less malleable than the pure metal.

Write (three marks): (1) in the pure metal, layers of atoms slide over one another easily; (2) in the alloy, atoms of a different size disrupt the regular arrangement; (3) this disruption prevents the layers from sliding, making the alloy harder.

Watch out: the mark scheme deducts a mark if you never mention layers/rows/sheets of atoms — you must use that language. It also rejects "molecules", "intermolecular forces", "ionic bonds", or "covalent bonds" as the reason layers cannot slide; stick to atoms/cations and their arrangement. Saying the metallic bonds are stronger is explicitly ignored.