Metallic bonding and giant structures

Metallic bonding

A metal is a giant lattice of positive ions in a 'sea' of delocalised electrons. Metallic bonding is the strong electrostatic attraction between the positive ions and the delocalised electrons. It explains:

• electrical conductivity: delocalised electrons move when a voltage is applied
• high melting points: strong attraction acts throughout the lattice, stronger with more delocalised electrons and smaller ions
• malleability: layers of ions can slide without breaking the bonding

Diamond

Each carbon is covalently bonded to four others in a tetrahedral giant lattice. Very hard, very high melting point, does not conduct electricity (no delocalised electrons). Used in cutting tools.

Graphite and graphene

Graphite: each carbon bonds to three others in flat hexagonal layers; the fourth electron is delocalised, so graphite conducts along the layers. Weak forces between layers let them slide, so it is soft and used in pencils and as a lubricant, and in electrodes.

Graphene: a single layer of graphite. Extremely strong, light and an excellent conductor; used in electronics and composites.

Comparing structures

Worked example

Explain why graphite conducts electricity but diamond does not.

1. In graphite each C uses three electrons in bonds, leaving one delocalised electron per atom.
2. In diamond all four outer electrons are in covalent bonds.

Answer: Graphite has delocalised electrons that can move; diamond has none.

Check yourself

1. What is metallic bonding?
   • The electrostatic attraction between positive metal ions and delocalised electrons
   • Sharing of electron pairs between metal atoms
   • Attraction between positive and negative ions
   • Weak forces between metal atoms
   Show answer

   The electrostatic attraction between positive metal ions and delocalised electrons. That is the specification definition.

2. Why does magnesium have a higher melting point than sodium?
   • Mg is a giant covalent element
   • Mg has weaker metallic bonding
   • Mg2+ ions have a greater charge and each atom provides two delocalised electrons
   • Mg atoms are larger
   Show answer

   Mg2+ ions have a greater charge and each atom provides two delocalised electrons. Stronger attraction between ions and more delocalised electrons.

3. Why can graphite be used as a lubricant?
   • Its layers are held by weak forces and slide over each other
   • It has a very high melting point
   • It conducts electricity
   • It is made of carbon
   Show answer

   Its layers are held by weak forces and slide over each other. The weak forces between layers are easily overcome.

4. How many other carbon atoms is each carbon atom covalently bonded to in diamond?
   Show answer

   4. Each C forms four bonds in a tetrahedral arrangement.

5. What is graphene?
   • A form of diamond
   • A single layer of carbon atoms arranged in hexagons
   • A metal alloy of carbon
   • A simple molecular form of carbon
   Show answer

   A single layer of carbon atoms arranged in hexagons. Graphene is one layer of graphite, one atom thick.

6. Why are metals malleable?
   • The delocalised electrons are fixed
   • The ions repel strongly when layers move
   • Metals contain covalent bonds
   • Layers of positive ions can slide over each other without the bonding breaking
   Show answer

   Layers of positive ions can slide over each other without the bonding breaking. The delocalised electrons keep holding the ions as layers move.

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Sources

• Pearson Edexcel IAL Chemistry (2018) scheme of work
• Pearson Edexcel International Advanced Level Chemistry (2018) qualification page
• Pearson IAL Chemistry (2018) transition guide

Last updated 7 November 2026. Spotted a mistake? Tell us.