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1.5.5Physical Chemistry

Metallic Bonding — Edexcel AS Chemistry Revision Notes & Topical Questions

5 min read 5 parts Lesson 21 of 42

📚 Edexcel AS Chemistry Hub / Topical Revision
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Part 1 of 5The Metallic Bond Model

1.5.5 Metallic Bonding
Positive ions
  • Metal atoms lose their outer electrons to form positive ions arranged in a regular lattice.
Delocalised electrons
  • Outer-shell electrons are free to move throughout the structure, forming a sea of mobile negative charge.
Electrostatic attraction
  • The strong attraction between the positive ions and the delocalised electrons is the metallic bond.
Non-directional bond
  • The bonding acts in all directions, so metal ions can shift position without the structure falling apart.

Part 2 of 5Factors Affecting Strength

Factors Affecting Strength
Ionic charge
  • A higher charge on the ion, such as Mg²⁺ compared with Na⁺, gives stronger attraction and a higher melting point.
Number of delocalised electrons
  • Magnesium releases two electrons per atom whereas sodium releases one, so more electrons strengthen the bond.
Ionic radius
  • Smaller ions have a higher charge density and attract the delocalised electrons more strongly.
Resulting trend
  • Melting points across period 3 rise from Na to Al as charge increases and radius decreases.
MetalIonRelative strength of bonding
NaNa⁺Weaker
MgMg²⁺Stronger
AlAl³⁺Strongest of the three

Part 3 of 5Explaining Physical Properties

Electrical conductivity
  • Delocalised electrons move through the lattice when a voltage is applied, carrying charge in both solid and liquid metals.
Thermal conductivity
  • Mobile electrons and vibrating ions pass kinetic energy quickly through the metal.
Malleability and ductility
  • Layers of ions slide over each other and the sea of electrons keeps holding them together.
High melting point
  • A lot of energy is needed to overcome the strong attraction between the ions and the electrons.

Part 4 of 5Describing the Structure

1
Start with a metal atom, such as magnesium, with two outer electrons in its highest energy level.
2
The atoms lose these outer electrons, which become delocalised and move freely between the particles.
3
The remaining Mg²⁺ ions pack together in a regular giant lattice.
4
The sea of electrons attracts all the positive ions equally and holds the lattice together.
5
When a force is applied, layers of ions slide but bonding is maintained, so the metal bends instead of breaking.

Part 5 of 5Exam Checklist & Tips

1.5.5 – Key Points for the Exam

  • Metallic bond Electrostatic attraction between positive metal ions and delocalised electrons.
  • Delocalised electron An electron not fixed to one atom but free to move through the structure.
  • Malleable Able to be hammered or bent into shape without breaking.
  • Giant metallic lattice A regular arrangement of positive ions surrounded by a sea of electrons.

Common Mistakes

  • Saying the electrons are shared between two specific atoms; they are delocalised across the structure.
  • Stating that metals contain free atoms; they contain positive ions.
  • Forgetting to mention both the ion charge and the number of delocalised electrons when comparing strength.
  • Explaining conduction as movement of ions in a solid metal; it is the electrons that move.

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