Alloys and their properties
Why alloys are harder than pure metals, and examples including brass and steel.
Review these first
Learning objectives
What you need to be able to do
Teacher-mapped phrasing — check against the official Cambridge syllabus for exact wording.
- 9.3.1Describe an alloy and explain in terms of structure why alloys are harder than pure metals.
5 minute read
Alloys
An alloy is a mixture of a metal with one or more other elements — usually other metals, or sometimes carbon — designed to improve on the properties of the pure metal alone.
Why alloys are harder than pure metals
In a pure metal, all the atoms are the same size, arranged in regular layers that can slide over each other relatively easily — which is why pure metals tend to be comparatively soft.
In an alloy, atoms of a different element (a different size) are mixed in among the original metal atoms. This disrupts the regular layered structure, so the layers can no longer slide past each other as smoothly. The result is that alloys are generally harder and stronger than the pure metals they are made from.
Common alloys
- Brass (copper + zinc) — harder than pure copper, used for fittings, musical instruments.
- Steel (iron + carbon, sometimes with other metals) — much harder and stronger than pure iron, used in construction and manufacturing.
- Bronze (copper + tin) — harder and more corrosion-resistant than pure copper, used for statues and some tools.
Alloys are chosen deliberately: pure metals are often too soft for demanding structural uses, so mixing in a small amount of another element solves the problem while retaining most of the useful properties (like conductivity) of the original metal.
Think of it like this
A pure metal is like a stack of identical, smooth coins that slide over each other easily when you push the stack sideways. An alloy is like the same stack with a few odd-sized buttons mixed in — suddenly the stack jams and resists sliding, because the buttons do not fit the smooth layered pattern the coins had.
Common misconceptions
- Thinking an alloy is a compound. It is a mixture — the different elements are not chemically bonded together in fixed proportions, they are simply mixed together in the solid structure.
- Believing any mixture of metals automatically makes something harder. It is specifically the disruption of the regular layered arrangement, caused by atoms of different sizes, that increases hardness.
- Assuming alloying always improves every property. Alloys are usually harder and stronger, but this can come at the cost of properties like conductivity, which is often slightly reduced compared with the pure metal.
In the exam
- A full explanation of alloy hardness needs the causal chain: different-sized atoms → disrupted regular layers → layers cannot slide as easily → harder material. Skipping the middle step is a common way to lose a mark.
- When naming an alloy's components, be precise — brass is copper and zinc, not copper and tin (that is bronze) — these are commonly mixed up.