2.4.3—Alloys
- Syllabus
- First assessment 2025
- Objective
- 2.4.3
- Level
- HL
Alloy Structure and Properties
An alloy is a mixture containing a metal and one or more other metals or non-metals. Different-sized atoms disrupt the regular lattice, making layer sliding more difficult while non-directional metallic bonding remains.
Explain an alloy property by referring to composition, lattice disruption, and the restricted movement of layers; do not call the alloy a compound.
In brass, differently sized Cu and Zn atoms disturb regular layer alignment, so dislocations move less easily and the alloy can be harder than pure copper. Material choice still involves trade-offs—an alloy may gain strength while losing ductility or conductivity—and its variable composition confirms that it is a mixture.
Explaining Alloy Properties
Assessment in practice
Representative question
Question 1
[Maximum number: 3]
Explain why metals alloyed with another metal are usually harder and stronger but poorer conductors than the pure metal.
metal ions/atoms have different sizes cations/atoms/layers do not slide over each other as easily «irregularities» obstruct free movement of electrons
Marking guidance:
Accept electrons move less easily/less delocalized for M3.
Models to Materials Summary
Retrieve the pathway: locate bonding contributions, connect them to material properties, distinguish alloy lattice disruption, and construct addition or condensation polymer repeating units from monomer evidence.
Check that the bonding description matches the material, the property explanation names the structural cause, and every polymer substituent, continuation bond, and released small molecule is represented.