2.3.1 Nature of Metallic Bonding
The electrostatic attraction between a lattice of positive ions and delocalized electrons.
The 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.
Interactive Model: The "Sea of Electrons"
Non-Directional Bonding
Unlike covalent bonds (which are directional) or ionic bonds (which effectively lock ions in place), metallic bonding acts in all directions.
The attraction exists between any cation and the surrounding delocalized electrons. This property is crucial for understanding malleability.
Delocalization
The electrons are not associated with any single atom. They are mobile charge carriers.
- 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.
Electrical
When a potential difference is applied, electrons flow towards the positive terminal, carrying charge.
Thermal
Mobile electrons gain kinetic energy and move rapidly to cooler parts of the lattice, transferring heat energy.
Exam Tip: Distinguish this from ionic conductivity! In molten salts, ions move. In metals, electrons move.
Malleability & Ductility
Metals can be hammered into sheets (malleable) or drawn into wires (ductile) without breaking.
The "Sliding Layers" Mechanism
Because the metallic bond is non-directional, the attractive forces remain intact even when the atoms move. 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 Compounds: In ionic lattices, shifting layers brings ions of like charge (e.g., + and +) together. The resulting repulsion causes the crystal to shatter (brittle).
Lustre (Shiny Appearance)
Delocalized electrons can absorb and re-emit light across a wide range of wavelengths, giving metals their characteristic shiny appearance.