Metallic bonding
Metallic bonding
Metallic bonding and mobile electrons
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A metal contains a giant lattice of positive ions surrounded by delocalised electrons. 'Delocalised' means the electrons are not restricted to one atom or one bond.
The attraction between the positive ions and these electrons holds the metal together. Strong attractions often give metals high melting and boiling points.
The delocalised electrons can move and carry charge in both solid and liquid metals. The positive ions do not travel through the solid to conduct electricity.
Metals do not normally dissolve as intact metallic lattices in molecular solvents. A metal reacting with a substance is a different process.
- Metallic bonding
- Strong electrostatic attraction between positive metal ions and delocalised electrons.
- Delocalised electron
- An electron not confined to one atom or one bond, able to move through the structure.
🧪 TEST IT
Work on paper. Attempt each question before opening its answer. These are original CrackingChem questions, written in AQA style.
- Define metallic bonding. [3]
- Explain why solid magnesium conducts electricity. [2]
- Explain why magnesium has a relatively high melting point. [2]
Total: 7 marks
Show answer & marking points
- Strong electrostatic attraction [1] between positive metal ions [1] and delocalised electrons [1].
- Delocalised electrons are mobile [1] and carry charge through the solid lattice [1].
- Strong attractions between positive ions and delocalised electrons [1] require substantial energy to overcome [1].
Sodium chloride and magnesium
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Sodium chloride and magnesium both have giant structures with strong electrostatic attractions. The difference is what is attracting what.
In sodium chloride, positive sodium ions attract negative chloride ions. In magnesium, positive metal ions attract delocalised electrons.
This explains their different conductivity patterns. Magnesium already has mobile electrons in the solid. Solid sodium chloride has ions, but they cannot move through the lattice until it melts or dissolves.
| Feature | Sodium chloride | Magnesium |
|---|---|---|
| Particles | Na+ and Cl- ions | Mg2+ ions and delocalised electrons |
| Solid | Does not conduct: ions fixed | Conducts: delocalised electrons mobile |
| Molten | Conducts: ions mobile | Conducts: delocalised electrons mobile |
🧪 TEST IT
Work on paper. Attempt each question before opening its answer. These are original CrackingChem questions, written in AQA style.
- State the particles present in barium fluoride, BaF2, and in potassium metal. [2]
- Explain why solid potassium conducts electricity but solid barium fluoride does not. [4]
- Both substances conduct when molten. State the mobile charge carrier in each liquid. [2]
Total: 8 marks
Show answer & marking points
- BaF2: Ba2+ and F- ions [1]. Potassium: K+ ions and delocalised electrons [1].
- In solid BaF2 the ions are fixed [1], so there are no mobile charge carriers [1]. Potassium has mobile delocalised electrons [1] that carry charge [1].
- Ba2+ and F- ions in molten BaF2 [1]; delocalised electrons in molten potassium [1].