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wise otter.Chemistry
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K324 / 2027
Bonding and Structure

Lesson 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.

  • I can describe metallic bonding.Syllabus

    Syllabus K324, 3.3(a). Describe metallic bonding

  • I can explain the general properties of metals.Syllabus

    Syllabus K324, 3.3(b). Explain the general properties of metals

  • I can recognise an alloy.Syllabus

    Syllabus K324, 3.4(b). Recognise an alloy

  • I can identify metals and alloys in diagrams.Syllabus

    Syllabus K324, 3.4(c). Identify metals and alloys in diagrams

  • I can explain changed properties of alloys.Syllabus

    Syllabus K324, 3.4(d). Explain changed properties of alloys

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 understanding

Why is "the larger atoms are harder" a poor explanation for an alloy being harder than the pure metal?

  1. The different-sized atoms disrupt the regular layers, so the layers cannot slide easily.
  2. The larger atoms form covalent bonds with the metal, and covalent bonds are stronger.
  3. The larger atoms fill the gaps, so the alloy has no delocalised electrons left.
Show the answer

The different-sized atoms disrupt the regular layers, so the layers cannot slide easily.

Hardness comes from the arrangement. Atoms of a different size distort the layers, which makes it harder for layers to slide. A single atom is not hard or soft.

Check your understanding

Four diagrams show particles in a solid. Which one represents an alloy?

  1. Identical circles packed in regular rows with no gaps between them
  2. Alternating circles marked + and - in a regular repeating pattern
  3. Small separate pairs of joined circles, spaced far apart from each other
  4. Regular rows of identical circles with a few larger, different circles in between
Show the answer

Regular rows of identical circles with a few larger, different circles in between

An alloy is a metal mixed with another element, so it has two kinds of atom, and the different sizes break up the regular rows.

Check your understanding

Copper is used for electrical wires and for the bases of cooking pots. Which properties suit both uses?

  1. It has a low melting point and is a poor conductor of heat
  2. It is soft, has a low density and reacts readily with cold water
  3. It is brittle and conducts electricity when molten but not when solid
  4. It conducts electricity and heat well, is malleable and has a high melting point
Show the answer

It conducts electricity and heat well, is malleable and has a high melting point

Wires need a good electrical conductor that can be drawn and bent. Pot bases need a good heat conductor that does not melt on a stove.

Pure only

Exam-style question

(a) Explain, in terms of structure and bonding, why copper has a high melting point and conducts electricity when solid. [3]
(b) Brass is an alloy of copper and zinc. Explain why brass is harder than pure copper. [2] [5]

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