Skip to notes
wise otter.Chemistry
Contents
Bonding and Structure

Topic 5 of 6

Metals and alloys

Recognize metals and alloys and connect their properties to their arrangement.

O-Level 2026 SEC G3 2027. Extensions are labelled Pure only.

Metals and alloys: properties from arrangement

Recognize a metal and an alloy, then connect structure to their different behaviour.

Metals generally have high melting and boiling points, conduct heat and electricity, and are malleable: they can be hammered into shape. Most are solids at room temperature. These are general patterns, not rules without exceptions.

Pure only

In a metal, positive ions occupy a lattice surrounded by delocalised electrons. These electrons are free to move throughout the metal. Metallic bonding is the strong electrostatic attraction between the positive ions and the delocalised electrons.

Pure only

Positive ions in delocalised electrons

A metallic structureTwelve positive metal ions form a regular arrangement. Twelve electron symbols lie between them, not attached to specific ions. Metallic bonding is the electrostatic attraction between the positive ions and delocalised electrons. Particle numbers and charges are schematic, not a particular metal formula.++++++++++++
Delocalised electrons can move through the structure. They are not confined to one atom or one bond.
  • Positive metal ion
  • Delocalised electron

A simplified two-dimensional fragment, not to scale. Plus signs indicate positive charge, not a specified ion charge. The electron count is illustrative.

Moving electrons carry charge. When layers of ions slide, attraction to the delocalised electrons continues, so the metal can change shape.
Pure only
Explaining metallic properties
PropertyStructural explanation
High melting pointMuch energy is needed to overcome the strong metallic bonding.
Electrical conductivityDelocalised electrons move and carry charge, in both solid and molten metal.
Thermal conductivityMobile electrons transfer energy rapidly through the metal; lattice vibrations also transfer energy.
MalleabilityLayers can slide while metallic attraction holds the structure together.

An alloy is a mixture of a metal with other elements. Brass contains copper and zinc. Stainless steel contains iron and chromium, with other elements depending on its composition. Unlike a compound, an alloy need not have a fixed ratio of elements.

Pure metal: regular layers

Equal-sized atoms in regular rowsThirteen equal-sized particle symbols are arranged in regular offset rows. This compares atomic sizes and arrangement; the delocalised electrons are omitted.
One type of atom, arranged in regular layers.

Alloy: disrupted layers

A different-sized atom distorts the regular arrangementThirteen particle symbols include one larger amber atom. The smaller neighbouring atoms are displaced, so the layers are less regular. This compares atomic sizes and arrangement; the delocalised electrons are omitted.
Different-sized atoms disrupt the regular arrangement.

A simplified substitutional alloy, not to scale. Other alloys may contain smaller atoms in gaps.

A pure metal contains one type of atom. An alloy contains more than one; differently sized circles represent its different constituent atoms.
Pure only

Different-sized atoms disrupt the regular arrangement. Layers slide less easily, so alloys are often harder and less malleable than the pure metal. Their melting behaviour can also differ. The explanation must fit the property: disrupted layers explain hardness, not every possible difference between an alloy and its constituents.

Pure only
Check your understandingWhy is "the larger atoms are harder" a poor explanation for an alloy being harder?Think it through, then reveal the answer
The key is the arrangement: different-sized atoms distort the regular layers and hinder sliding. Hardness is a property of the material, not a claim that an individual larger atom is harder.