Metallic Bonding

This lesson covers metallic bonding as required by the AQA GCSE Combined Science Trilogy specification (8464), section 4.2.3. You need to understand the structure of metals, the nature of the metallic bond, and how this structure explains the properties of metals.

What Is Metallic Bonding?

Metallic bonding is the strong electrostatic force of attraction between positive metal ions (cations) and a "sea" of delocalised electrons.

In a metal:

Metal atoms lose their outer shell electrons, forming positive ions.
The lost electrons become delocalised — they are no longer associated with any particular atom and are free to move throughout the entire structure.
The positive metal ions are arranged in a regular lattice (a repeating pattern).
The delocalised electrons move freely between the ions, forming a "sea of electrons."
The strong electrostatic attraction between the positive ions and the sea of negative electrons holds the structure together.

$\text{Metal atoms} \rightarrow \text{Positive metal ions (M}^{n+}\text{)} + \text{Delocalised electrons (e}^-\text{)}$

graph TD
    A["Metallic Bonding"] --> B["Positive metal ions<br/>arranged in a<br/>regular lattice"]
    A --> C["Sea of delocalised<br/>electrons free to<br/>move throughout"]
    B --> D["Strong electrostatic<br/>attraction between<br/>ions and electrons"]
    C --> D
    D --> E["This is the<br/>METALLIC BOND"]

    style A fill:#2c3e50,color:#fff
    style B fill:#e74c3c,color:#fff
    style C fill:#3498db,color:#fff
    style D fill:#f39c12,color:#fff
    style E fill:#27ae60,color:#fff

Exam Tip (AQA 8464): The precise definition is: "Metallic bonding is the strong electrostatic force of attraction between positive metal ions and delocalised electrons." Make sure you include all three key parts: (1) electrostatic attraction, (2) positive metal ions, and (3) delocalised electrons.

Structure of Metals

Metals have a giant metallic structure:

The positive ions are arranged in a regular lattice — a repeating 3D pattern.
The delocalised electrons occupy the spaces between the ions and are free to move throughout the structure.
The metallic bond is strong because it involves the attraction between positively charged ions and negatively charged delocalised electrons.
The metallic bond acts in all directions — it is non-directional.

Properties of Metals Explained by Metallic Bonding

1. High Melting and Boiling Points

Most metals have high melting and boiling points because:

The electrostatic attraction between positive metal ions and delocalised electrons is strong.
A large amount of energy is required to overcome these strong metallic bonds.

The strength of metallic bonding depends on:

The charge on the metal ion — higher charges create stronger attractions.
The size of the metal ion — smaller ions pack more closely, creating stronger attractions.
The number of delocalised electrons — more delocalised electrons create a stronger "sea."

Metal	Ion Charge	Delocalised Electrons per Atom	Melting Point (°C)
Sodium (Na)	+1	1	98
Magnesium (Mg)	+2	2	650
Aluminium (Al)	+3	3	660
Iron (Fe)	+2/+3	2	1538

Exam Tip: Magnesium has a higher melting point than sodium because Mg²⁺ ions have a greater charge than Na⁺ ions, and magnesium contributes 2 delocalised electrons per atom compared to sodium's 1. This creates stronger electrostatic attraction.

2. Good Electrical Conductivity

Metals are good conductors of electricity because:

The delocalised electrons are free to move throughout the structure.
When a potential difference is applied, the electrons flow in one direction, carrying charge.

3. Good Thermal Conductivity

Metals are good conductors of heat because:

Delocalised electrons gain kinetic energy when heated and move rapidly through the structure, transferring energy to other parts of the metal.
The closely packed ions also transfer vibrations to neighbouring ions.

4. Malleability and Ductility

Metals are malleable (can be hammered into shape) and ductile (can be drawn into wires) because:

The layers of positive ions can slide over each other when a force is applied.
The delocalised electrons can redistribute and maintain the metallic bonding in the new positions.
The structure does not break apart — the metallic bond is maintained.

graph LR
    A["Force applied<br/>to metal"] --> B["Layers of ions<br/>slide over<br/>each other"]
    B --> C["Delocalised electrons<br/>redistribute around<br/>ions in new positions"]
    C --> D["Metallic bond<br/>maintained —<br/>metal bends,<br/>does not shatter"]

    style A fill:#e74c3c,color:#fff
    style B fill:#f39c12,color:#fff
    style C fill:#3498db,color:#fff
    style D fill:#27ae60,color:#fff

Exam Tip: This is the key difference between metals and ionic compounds. In metals, layers can slide because the delocalised electrons maintain the bond. In ionic compounds, layers cannot slide because displacing them brings like charges together, causing repulsion and shattering.