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Metallic Bonding

Metallic bonding: sea of delocalised electrons, layers of ions, alloys, and how these explain conductivity, malleability, and strength.

  • SEC G3 Pure Chemistry 2027
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Learning objectives

  • describe metals as a lattice of positive ions in a ‘sea of electrons’
  • describe the general physical properties of metals as solids having high melting and boiling points, malleable, good conductors of heat and electricity in terms of their structure (see also 3.4(g)).
  • describe an alloy as a mixture of a metal with another element, e.g. brass; stainless steel
  • identify representations of metals and alloys from diagrams of structures
  • explain why alloys have different physical properties to their constituent elements

Metallic properties make sense when you connect them to delocalised electrons and the layers of positive ions in the lattice.

1. Definition

Metallic bonding is the strong electrostatic force of attraction between the positive metal ions and the sea of delocalised electrons.

2. Key Ideas

  • Metals have a giant metallic structure: positive ions in layers + delocalised electrons between them.
  • Metals conduct electricity because electrons are mobile.
  • Metals are malleable/ductile because layers of ions can slide without breaking the metallic bond.
  • Alloys are mixtures; different-sized atoms disrupt layers and make sliding harder → stronger/harder.

3. Detailed Explanations

Quick Recall (metal answers)
  • Metals: positive ions in layers + delocalised electrons between layers.
  • Conducts electricity because electrons are mobile.
  • Malleable/ductile because layers can slide while attraction remains.
  • Alloys are mixtures; different-sized atoms disrupt layers and block sliding.

A. What “Delocalised” Means

Delocalised electrons are electrons that are not attached to any one atom. They can move through the whole metal.

The metal atoms become positive ions arranged in a regular lattice (layers).

Metallic bonding structure Metallic bonding: a regular lattice of positive ions is held together by electrostatic attraction to mobile mobile electrons.++++++++++++++++++++++++e⁻e⁻e⁻e⁻e⁻e⁻e⁻e⁻e⁻e⁻e⁻e⁻e⁻e⁻e⁻mobile electrons can move through the structurepositive ionsmobile electronsattraction inall directions
Metallic bonding: a regular lattice of positive ions is held together by electrostatic attraction to mobile mobile electrons.

B. Properties of Metals (Write This Table in Your Head)

PropertyWhat you observeMark-scheme explanation
Electrical conductivityConducts as a solid and when moltenDelocalised electrons are mobile and carry charge
Thermal conductivityConducts heat wellMobile electrons transfer energy quickly through the metal
High melting/boiling point (most metals)Usually highStrong electrostatic attraction between positive ions and delocalised electrons requires lots of energy to overcome
Malleable and ductileCan be hammered / drawn into wiresLayers of positive ions can slide; attraction to delocalised electrons remains so the structure stays together
Alloy conductivity (common fact)

Alloys are usually less conductive than pure metals because different-sized atoms disrupt the regular lattice and scatter the delocalised electrons.

Recall: ionic vs metallic conductivity

Ionic compounds conduct only when ions are mobile (molten/aqueous). Metals conduct because electrons are mobile. See Ionic Bonds.

C. Alloys (Why They Are Harder/Stronger)

An alloy is a mixture of a metal with one or more other elements (e.g., brass is Cu + Zn).

  • Pure metal: identical ions in neat layers → layers slide easily.
  • Alloy: different-sized atoms/ions disrupt the layers → layers cannot slide easily → harder/stronger.

See Elements, Compounds & Mixtures for “alloys are mixtures”.

Pure metal and alloy layer comparison Pure-metal layers contain similar-sized particles and can slide. Different-sized particles in an alloy disrupt the regular layers, making sliding more difficult.Pure metalAlloyregular layers slide more easilydifferent sizes disrupt sliding
Pure-metal layers contain similar-sized particles and can slide. Different-sized particles in an alloy disrupt the regular layers, making sliding more difficult.

4. Common Mistakes

  • Saying metals conduct because “ions move”. In metals, electrons carry charge.
  • Saying alloys are compounds (wrong). Alloys are mixtures (no fixed ratio).
  • Writing “metals become stable noble gases” (wrong). They form a stable structure due to metallic bonding; do not force the noble-gas language.
  • Forgetting the sliding-layers explanation for malleability/ductility.
  • Claiming all metals have high melting points (unsafe: mercury is liquid at room temperature). Write “most metals”.

5. Exam Tips

Definition that scores

“Strong electrostatic attraction between positive metal ions and delocalised electrons.”

Property keywords

Conducts electricity: “delocalised electrons are mobile”.
Malleable/ductile: “layers slide; attraction remains”.

6. Worked Examples

Modelled example 1

Malleability (Sliding Layers)

Core

Problem

Explain why pure metals are malleable.
Study the worked solution

  1. Describe the structure

    Method

    Identify regular layers of positive metal ions.

    Reason

    Identical ions in a pure metal form an ordered giant metallic structure.

    Working

    Positive ions are arranged in regular layers surrounded by delocalised electrons.

  2. Apply a force

    Method

    Allow one ion layer to slide past another.

    Reason

    The layers can change relative position without requiring fixed directional bonds between particular ions.

    Working

    Force applied → ion layers slide.

  3. Explain why the metal remains together

    Method

    Retain electrostatic attraction after sliding.

    Reason

    Positive ions remain attracted to the sea of delocalised electrons in their new positions.

    Working

    The structure changes shape without the metallic bonding being lost.

Guided practice 2

Conductivity (What Carries Charge?)

About 5 min

Problem

Explain why a solid metal conducts electricity.

Identify both the carrier and its mobility

Charge carrier
Required property

Hints

Hint 1: distinguish metal from ionic conduction
The positive ions remain in lattice positions in a solid metal.
Hint 2: use the definition of delocalised
A delocalised electron is not attached to one atom and can move through the structure.
View solution step by step

  1. Name the charged particles

    Method

    Identify delocalised electrons.

    Reason

    Outer electrons are shared across the giant metallic structure rather than fixed to individual atoms.

    Working

    Charge carriers = delocalised electrons.

  2. Connect mobility to current

    Method

    State that the electrons move through the metal.

    Reason

    Moving charged particles transfer charge and produce an electric current.

    Working

    Mobile delocalised electrons → electrical conduction.

Common misconception 3

Error Analysis (Fix the Student)

Find and correct the mistake

Learner response

A student writes: “Alloys are stronger because they have stronger metallic bonds.” Locate the unsupported claim and correct the explanation.

Identify the structural change

Effect of alloy atoms
Result for layer motion

View solution step by step

  1. Locate the unsupported claim

    Method

    Reject the assumption that alloying automatically strengthens metallic attraction.

    Reason

    The supplied comparison is explained by how layers move, not by evidence for a larger bond strength.

    Working

    “Stronger metallic bonds” is not established by the alloy label.

  2. Use the alloy structure

    Method

    Introduce different-sized atoms into the regular layers.

    Reason

    They distort the layers and obstruct their relative motion.

    Working

    Different sizes → disrupted layers → harder sliding.

  3. Write the correction

    Working

    Alloys are usually harder because their disrupted layers cannot slide easily.

Examiner practice 4

Alloy Hardness (Brass vs Copper)

3 marks

Examination question

Brass is an alloy of copper and zinc. Explain why brass is harder than pure copper. [3 marks]

Write a linked structural comparison

View solution step by step

  1. Describe pure copper

    1 mark

    Method

    Identify identical atoms in regular layers.

    Reason

    Uniform layers can slide over one another relatively easily.

    Working

    Pure copper: regular layers → easier sliding.

  2. Describe brass

    1 mark

    Method

    Identify differently sized copper and zinc atoms.

    Reason

    The size difference distorts the regular layer arrangement.

    Working

    Brass: disrupted layers.

  3. Link structure to hardness

    1 mark

    Method

    Compare how readily the layers move.

    Reason

    Layers that cannot slide easily resist permanent shape change.

    Working

    Brass is harder than pure copper.

Challenge 5

Data Interpretation (Choose the Best Material)

Minimal support

Design transfer

A wire must conduct electricity well while solid and be easily drawn into shape. Choose a metal or an ionic compound and justify both required properties at particle level.

Test both requirements

Best material class
Solid charge carrier

Hints

Hint 1: test solid conductivity
In a solid ionic lattice, the ions are not mobile.
Hint 2: test shape change
Ductility requires layers to move while the structure remains bonded.
View solution step by step

  1. Choose the material

    Method

    Select a metal.

    Reason

    A metal satisfies both conductivity and ductility in the solid state.

    Working

    Choice: metal.

  2. Justify conductivity

    Method

    Use mobile delocalised electrons.

    Reason

    They move through the solid structure and carry charge.

    Working

    Mobile electrons → solid-state conduction.

  3. Justify ductility

    Method

    Use sliding ion layers with continued attraction.

    Reason

    Layers can move while positive ions remain attracted to delocalised electrons.

    Working

    The metal can be drawn into wire without its metallic structure separating.

7. Mind Stretchers

Mind stretcher 1: Why Are Alloys Less Malleable?Extension

Question: Explain why alloys are usually less malleable than pure metals, even though both have delocalised electrons.

Show Answer

Both have delocalised electrons, but malleability depends on whether layers can slide.

Alloys contain different-sized atoms that distort the regular layers and block sliding, so they are less malleable.

Mind stretcher 2: Conductivity Trap (Molten Ionic vs Solid Metal)Extension

Question: A student says: “Both molten sodium chloride and solid copper conduct electricity for the same reason.” Explain why this is wrong.

Show Answer

Molten NaCl conducts because ions are mobile and carry charge.

Solid copper conducts because delocalised electrons are mobile and carry charge.

8. Quiz

Quiz time

Ready to check your understanding? Try the interactive quiz, then review any questions you missed.

Go to quiz