Nature of Metallic Bonding
The electrostatic attraction between cations and delocalized electrons.
Definition
A metallic bond is the electrostatic attraction between a lattice of positive ions (cations) and delocalized valence electrons.
Key Concept: The valence electrons "detach" from their parent atoms, becoming free to move throughout the entire structure. The remaining atoms become positive ions (cations), held together by their attraction to this "sea" of negative electrons.
The "Sea of Electrons" Model
Non-Directional Bonding
Unlike covalent bonds (directional) or ionic bonds, metallic bonding acts in all directions. The attraction exists between any cation and the surrounding delocalized electrons.
Delocalization
- Group 1 (Na): 1 delocalized electron per atom.
- Group 2 (Mg): 2 delocalized electrons per atom.
- Group 13 (Al): 3 delocalized electrons per atom.
Physical Properties
Electrical & Thermal Conductivity
Metals are excellent conductors because the delocalized electrons are highly mobile.
Electrons flow towards positive terminal, carrying charge.
Mobile electrons gain KE and move rapidly to cooler parts of lattice.
Malleability & Ductility
When a force is applied, layers of cations can slide over each other. The "sea" of electrons moves with them, maintaining the electrostatic attraction and preventing the structure from shattering.
Contrast with Ionic: In ionic lattices, shifting layers brings ions of like charge together → repulsion → crystal shatters (brittle).
Lustre (Shiny Appearance)
Delocalized electrons can absorb and re-emit light across a wide range of wavelengths, giving metals their characteristic shiny appearance.
Exam Tip
Distinguish metallic conductivity from ionic conductivity! In molten salts, ions move. In metals, electrons move.