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S1.1 - Introduction to the particulate nature of matter S1.2 - The nuclear atom S1.3 - Electron configurations S1.4 - Counting particles by mass - The mole S1.5 - Ideal gases S2.1 - The ionic model S2.2 - The covalent model S2.3 - The metallic model S2.4 - From models to materials S3.1 - The periodic table - Classification of elements S3.2 - Functional groups - Classification of organic compounds R1.1 - Measuring enthalpy changes R1.2 - Energy cycles in reactions R1.3 - Energy from fuels R1.4 - Entropy and spontaneity AHL R2.1 - How much? The amount of chemical change R2.2 - How fast? The rate of chemical change R2.3 - How far? The extent of chemical change R3.1 - Proton transfer reactions R3.2 - Electron transfer reactions R3.3 - Electron sharing reactions R3.4 - Electron-pair sharing reactions

S2.4 - From models to materials

2.4.1 The Bonding Continuum 2.4.2 Using the Bonding Triangle 2.4.3 Alloys 2.4.4 Polymer and Plastic Properties 2.4.5 Addition Polymerization 2.4.6 Condensation Polymerization (AHL)

Alloys and Their Properties

Specification Reference S2.4.3

Quick Notes:

  • Alloys are mixtures of a metal with one or more other metals or non-metals.
  • They are held together by metallic bonding, which is non-directional – this allows atoms of different sizes to fit into the lattice.
  • Alloys often have improved properties compared to pure metals:
    • Greater strength
    • More corrosion resistance
    • Enhanced hardness or toughness
  • Common examples:
    • Bronze = copper + tin
    • Brass = copper + zinc
    • Stainless steel = iron + chromium + nickel

Full Notes:

What Is an Alloy?

An alloy is a homogeneous mixture of a metal with other elements (metals or non-metals).

Atoms of different elements are evenly distributed within the metallic lattice and all atoms are held by the same metallic bonding forces as pure metals.

Bonding in Alloys

Metallic bonding in alloys remains non-directional. Positive metal cations are surrounded by a sea of delocalized electrons in all directions.

Substituting or inserting different atoms disrupts the regular lattice of pure metals, preventing layers from sliding easily over each other. This increases strength and hardness.

For Example Pure copper vs bronze

Pure copper is softer and more malleable than bronze (an alloy of copper and tin).

In pure copper, all metal ions in lattice are the same (Cu), meaning the lattice has a regular structure and layers can easily slide over each other.

IB Chemistry diagram of pure copper metal showing a regular lattice of identical Cu ions with delocalized electrons allowing layers to slide.

However, in bronze, the copper and tin ions in the lattice have slightly different sizes, meaning the regular arrangement of ions gets disrupted and now the layers are unable to easily slide over each other.

IB Chemistry diagram of bronze alloy showing differently sized Cu and Sn ions disrupting the lattice so layers cannot slide easily.

This makes bronze harder and less malleable than pure copper.

Why Are Alloys Useful?

Compared to pure metals, alloys often have:

Property Explanation
Higher strength Distorted lattice prevents slippage of atomic layers
Greater hardness Atoms of different sizes reduce movement
Corrosion resistance Some alloys (e.g. stainless steel) form protective surface layers
Tailored properties Adjusting composition allows specific uses (tools, coins, wires)

Examples of Common Alloys

Alloy Components Typical Use and Benefit
Bronze Copper + Tin Harder than copper, used in tools, sculptures
Brass Copper + Zinc Corrosion-resistant, used in instruments, fittings
Stainless steel Iron + Chromium (+ Nickel) Resists rust, used in cookware and construction

Note: You are not required to memorise specific compositions.

Summary