Metals possess a unique type of chemical bonding that distinguishes them from both ionic salts and covalent molecules. This bonding allows metals to exhibit exceptional electrical conductivity and the ability to be shaped without breaking. The IGCSE 0654 Extended syllabus requires a detailed description of metallic bonding as an attraction between positive ions and a "sea" of delocalised electrons, and a rigorous explanation of how this structure results in the characteristic properties of metals.

A metallic bond is the electrostatic attraction between a giant lattice of positive metal ions and a "sea" of delocalised electrons.

The Microscopic Structure

1. Positive Ions: Metal atoms lose their outer-shell electrons to achieve stability. These atoms become positive ions (cations) arranged in a regular, giant lattice.
2. Delocalised Electrons: The lost electrons are not attached to any single atom. Instead, they are free to move throughout the entire structure. This collection of mobile electrons is often referred to as a "sea of delocalised electrons."
3. The Force: The bond is the strong attraction between the stationary positive ions and the mobile, negative delocalised electrons that surround them.

The presence of the "electron sea" provides a microscopic explanation for the macroscopic behavior of metals.

(a) Electrical and Thermal Conductivity

• Mechanism: Because the delocalised electrons are mobile, they can move through the giant metallic lattice when a potential difference (voltage) is applied.
• Consequence: This mobility allows metals to conduct electricity exceptionally well. Similarly, these electrons can transfer kinetic energy (heat) rapidly through the structure, making metals excellent thermal conductors.
• State: Unlike ionic compounds, which only conduct when liquid, metals conduct in both solid and liquid states because the electrons remain delocalised.

(b) Malleability and Ductility

• Mechanism: In a pure metal, the positive ions are arranged in regular layers. When a force is applied (e.g., hitting with a hammer), these layers can slide over one another.
• Structural Integrity: Crucially, as the layers slide, the "sea" of delocalised electrons moves with them. The electrostatic attraction remains constant, acting like a flexible "glue" that prevents the structure from shattering.
• Consequence: This allows metals to be malleable (hammered into sheets) and ductile (drawn into wires) without the bonds breaking.

Metallic bonding is a remarkably flexible and robust form of chemical attraction. By utilizing a shared pool of delocalised electrons, metal atoms create a giant lattice that is both incredibly strong and highly adaptable. This unique subatomic architecture is the reason metals are the primary materials used for the global electrical grid and the structural backbone of modern engineering.