What is metallic bonding and how does it differ from other types of chemical bonding?

Metallic bonding is a type of chemical bonding that occurs between atoms of metallic elements. It involves the sharing of free electrons among a lattice of metal atoms. Unlike ionic or covalent bonding, where electrons are transferred or shared between specific atoms, metallic bonding features a 'sea of electrons' that are delocalized and free to move throughout the structure. This gives metals their characteristic properties such as electrical conductivity and malleability.

How does metallic bonding contribute to the electrical conductivity of metals?

In metallic bonding, the delocalized electrons are free to move throughout the metal lattice. This mobility allows electrons to flow easily when an electric field is applied, making metals excellent conductors of electricity. The presence of these free-moving electrons is a key factor in the high electrical conductivity observed in metals.

Why are metals malleable and ductile due to metallic bonding?

Metals are malleable and ductile because the metallic bonding allows metal atoms to slide past each other without breaking the bond. The 'sea of electrons' acts as a cushion, maintaining the metallic bond even when the metal is deformed. This property enables metals to be hammered into sheets (malleability) or drawn into wires (ductility) without breaking.

What role does metallic bonding play in the thermal conductivity of metals?

Metallic bonding contributes to the high thermal conductivity of metals because the delocalized electrons can transfer kinetic energy rapidly throughout the metal lattice. As electrons move freely, they can quickly distribute heat energy, making metals effective at conducting heat. This is why metals are often used in applications requiring efficient heat transfer.

How does the strength of metallic bonding affect the melting and boiling points of metals?

The strength of metallic bonding directly influences the melting and boiling points of metals. Stronger metallic bonds, resulting from more delocalized electrons and a higher charge density, typically lead to higher melting and boiling points. This is because more energy is required to overcome the strong attractions between the metal ions and the sea of electrons, as seen in metals like tungsten and iron.

Why is "Calling the electrons 'free' rather than 'delocalised'." a common mistake in Metallic bonding?

Why it happens: Informal language. How to avoid it: Use the precise term: delocalised electrons. Source: 9701 Examiner Reports

Why is "Saying conduction in a metal is due to moving ions." a common mistake in Metallic bonding?

Why it happens: Confusing metals with molten ionic compounds. How to avoid it: In a solid metal the cations are fixed; the delocalised electrons carry the charge.

Why is "Describing the metal lattice as made of negative ions." a common mistake in Metallic bonding?

Why it happens: Charge confusion. How to avoid it: Metal ions are positive (cations) surrounded by negative electrons.

Why is "Thinking the metallic bonds break when a metal is bent." a common mistake in Metallic bonding?

Why it happens: Treating it like a brittle solid. How to avoid it: The layers slide and the bonds RE-FORM as electrons move with them — that's why metals deform instead of shattering. Source: 9701 Examiner Reports 2022-2024

Chemical Bonding(AS-Level Physical Chemistry)Cambridge International A Level Chemistry 9701

Metallic bonding

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Metallic Bonding — Cambridge International AS & A Level Chemistry 9701 (2025-2027 syllabus)

The 'sea of delocalised electrons' model, the precise definition, and how metallic bonding explains conductivity, high melting points and malleability — plus what makes some metals bond more strongly than others.

What you’ll learn

Mapped to the Cambridge International A Level 9701 syllabus (2025-2027).

3.3.1 — Define metallic bonding as the electrostatic attraction between positive metal ions and delocalised electrons.

The metallic bonding model

A lattice of positive metal ions sitting in a shared sea of delocalised outer electrons.

Definition. Metallic bonding is the electrostatic attraction between positive metal ions (cations) and the sea of delocalised electrons.

In a metal:

Each atom releases its outer-shell (valence) electrons, which become delocalised — no longer attached to one atom, but free to move throughout the structure.
This leaves a regular lattice of positive metal ions.
The strong attraction between the cations and the delocalised electron sea holds the metal together in all directions.

Delocalised electrons (red) move freely between fixed positive metal ions (blue).

Metallic bond = attraction between cations and delocalised electrons.
Outer electrons become delocalised (mobile).
Lattice of positive ions in an electron sea.

Explaining metallic properties

Mobile electrons → conductivity; strong attraction → high mp; sliding layers → malleability.

The model explains the typical properties of metals:

Electrical (and thermal) conductivity — the delocalised electrons are free to move and carry charge through the metal.
High melting and boiling points — the strong electrostatic attraction between cations and the electron sea needs a lot of energy to overcome.
Malleable and ductile — the layers of cations can slide over one another while the delocalised electrons maintain the bonding, so the metal bends/shapes rather than shatters.

What makes metallic bonding stronger?

More delocalised electrons per atom (higher cation charge): Mg²⁺ contributes 2 electrons vs Na⁺'s 1 → stronger bonding, higher mp.
Smaller ionic radius: the electron sea is held closer to the nuclei.

So magnesium has a much higher melting point than sodium (more delocalised electrons + smaller ion).

Conductivity: mobile delocalised electrons.
High mp: strong cation–electron attraction.
Malleable: layers slide, bonding maintained.
Stronger with more delocalised electrons + smaller ions.

How it’s examined

Usually 2-4 marks: the definition plus 'explain a property' (conductivity, melting point, malleability) and Period 3 melting-point trends (links to 9.1). Examiner reports flag 'free electrons' instead of 'delocalised', and explanations of conductivity that mention ions moving rather than electrons.

Sources: Cambridge International AS & A Level Chemistry 9701 syllabus (2025-2027), section 3.3; 9701 Examiner Reports 2022-2024; 9701/22 May/Jun 2024 question paper and mark scheme. Last reviewed 2026-05-20.

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Step-by-step worked examples — Metallic bonding

Step-by-step solutions to past-paper-style questions on metallic bonding, written exactly the way a tutor would explain them at the board.

1Explaining electrical conductivity (2 marks)
Getting started• conductivity
Question
Explain why metals conduct electricity in the solid state.
Step-by-step solution
1. Step 1
  Delocalised electrons are free to move throughout the metal lattice.
2. Step 2
  When a voltage is applied, these mobile electrons drift and carry charge → current flows.
Answer
Mobile delocalised electrons carry charge through the lattice.
Examiner tip
Unlike ionic solids, metals conduct as solids because it is the ELECTRONS (not ions) that move.
2Why metals are malleable (2 marks)
Getting started• malleability
Question
Explain why metals can be hammered into shape (malleable).
Step-by-step solution
1. Step 1
  Layers of positive ions can slide over each other when a force is applied.
2. Step 2
  The delocalised electrons move with them, so the metallic bonding is maintained and the metal does not shatter.
Answer
Layers of cations slide while the delocalised electrons keep the bonding intact.
3Period 3 metal melting points (3 marks)
Building confidence• melting point, trend
Question
Explain why the melting points increase Na < Mg < Al. (3)
Step-by-step solution
1. Step 1
  Delocalised electrons per atom increase: Na donates 1, Mg 2, Al 3.
2. Step 2
  Ionic charge increases (Na⁺, Mg²⁺, Al³⁺) and ionic radius decreases.
3. Step 3
  Stronger attraction between cations and the electron sea → more energy to melt → higher melting point.
Answer
More delocalised electrons + higher charge + smaller ions → stronger metallic bonding → higher melting point.
4Thermal conductivity of metals (3 marks)
Building confidence• thermal conductivity
Question
Explain why metals are good conductors of heat. (3)
Step-by-step solution
1. Step 1
  Heat gives the delocalised electrons more kinetic energy, so they move faster.
2. Step 2
  These mobile electrons travel through the lattice and collide with ions/other electrons.
3. Step 3
  Kinetic energy is transferred quickly along the metal → efficient heat conduction.
Answer
Mobile delocalised electrons gain and transfer kinetic energy rapidly through the lattice.
5Applying metallic bonding to a real metal (4 marks)
Stretch• application
Question
Aluminium is used for overhead power cables and for saucepans. Use metallic bonding to explain why it (a) conducts electricity and (b) can be shaped without shattering. (4)
Step-by-step solution
1. Step 1
  (a) Conductivity: Al³⁺ ions sit in a sea of delocalised electrons (3 per atom) that are free to move and carry current.
2. Step 2
  Many carriers: three delocalised electrons per atom make aluminium a particularly good conductor for its weight.
3. Step 3
  (b) Malleability: layers of Al³⁺ ions slide over each other when forced.
4. Step 4
  Bonding maintained: the delocalised electrons move with the layers, so the metallic bonds re-form and it doesn't crack.
Answer
Delocalised electrons carry current (conductivity); sliding layers with mobile electrons give malleability.
Examiner tip
Applied questions still want the model: name delocalised electrons, sliding layers, and bonding being maintained.
6Comparing two metals (4 marks)
Stretch• comparison, melting point
Question
Magnesium is harder and has a higher melting point than sodium. Explain this in terms of metallic bonding. (4)
Step-by-step solution
1. Step 1
  Delocalised electrons: Mg releases 2 per atom, Na only 1.
2. Step 2
  Ion charge and size: Mg²⁺ is smaller and more highly charged than Na⁺.
3. Step 3
  Attraction: the Mg²⁺ ions attract the denser electron sea far more strongly than Na⁺ does.
4. Step 4
  Consequence: stronger metallic bonding → harder solid and more energy needed to melt → higher melting point.
Answer
Mg²⁺ (2 delocalised e⁻, smaller, 2+ charge) bonds more strongly than Na⁺ → harder, higher m.p.

Key Formulae — Metallic bonding

The formulae you need to memorise for metallic bonding on the Cambridge International A Level 9701 paper, with every variable defined in plain English and a note on when to use it.

Strength of metallic bonding
$\text{metallic bond strength} \propto \frac{(\text{ionic charge}) \times (\text{delocalised e}^-\text{ per atom})}{\text{ionic radius}}$
$ionic charge$
charge on the metal cation (e.g. +1, +2, +3)
$delocalised e⁻$
number of outer electrons released per atom
$ionic radius$
size of the metal cation
When to use
Comparing hardness and melting points of metals: more electrons, higher charge and smaller ions → stronger bonding.

Key Definitions and Keywords — Metallic bonding

Definitions to memorise and the exact keywords mark schemes credit for metallic bonding answers — sharpened from recent examiner reports for the 2026 Cambridge International A Level 9701 sitting.

Metallic bond
Examiner keyword
The electrostatic attraction between a lattice of positive metal ions and the surrounding sea of delocalised electrons.
Delocalised electrons
Examiner keyword
Outer-shell electrons not associated with a single atom, free to move throughout the metallic lattice.
Giant metallic lattice
Examiner keyword
A regular 3D array of positive metal ions in a sea of delocalised electrons.
Malleable / ductile
Examiner keyword
Malleable = can be hammered into shape; ductile = can be drawn into wires; both arise because ion layers slide while bonding is maintained.

Common Mistakes and Misconceptions — Metallic bonding

The traps other students keep falling into on metallic bonding questions — taken from recent Cambridge International A Level 9701 examiner reports and mark schemes — and how to avoid them.

✕Calling the electrons 'free' rather than 'delocalised'.
9701 Examiner Reports
Why it happens
Informal language.
How to avoid it
Use the precise term: delocalised electrons.
✕Saying conduction in a metal is due to moving ions.
Why it happens
Confusing metals with molten ionic compounds.
How to avoid it
In a solid metal the cations are fixed; the delocalised electrons carry the charge.
✕Describing the metal lattice as made of negative ions.
Why it happens
Charge confusion.
How to avoid it
Metal ions are positive (cations) surrounded by negative electrons.
✕Thinking the metallic bonds break when a metal is bent.
9701 Examiner Reports 2022-2024
Why it happens
Treating it like a brittle solid.
How to avoid it
The layers slide and the bonds RE-FORM as electrons move with them — that's why metals deform instead of shattering.

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Metallic bonding

Short Study Notes in the form of Slides

Short Study Notes — Metallic bonding

Detailed Notes

What you’ll learn

How it’s examined

1Explaining electrical conductivity (2 marks)

2Why metals are malleable (2 marks)

3Period 3 metal melting points (3 marks)

4Thermal conductivity of metals (3 marks)

5Applying metallic bonding to a real metal (4 marks)

6Comparing two metals (4 marks)

Strength of metallic bonding

Metallic bond

Delocalised electrons

Giant metallic lattice

Malleable / ductile

✕Calling the electrons 'free' rather than 'delocalised'.

✕Saying conduction in a metal is due to moving ions.

✕Describing the metal lattice as made of negative ions.

✕Thinking the metallic bonds break when a metal is bent.

Practice questions

Past paper style quiz

Assess your understanding

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Metallic bonding — frequently asked questions