Metallic Bonding

1. High Melting and Boiling Points

• Explanation: To melt or boil a metal, the strong electrostatic forces of attraction between the positive ions and delocalised electrons must be overcome. This requires a significant input of thermal energy, which is why most metals are solids at room temperature and have high transition temperatures.

2. Electrical Conductivity

• Mechanism: Metals conduct electricity because the delocalised electrons are mobile and can carry an electric charge through the structure. When a potential difference (voltage) is applied, these electrons move towards the positive terminal, creating an electric current.

3. Thermal Conductivity

• Process: Heat is transferred through metals both by the vibration of ions and the rapid movement of delocalised electrons. The mobile electrons absorb kinetic energy and quickly transfer it to cooler parts of the lattice through collisions.

• Sliding Layers: Metals are described as malleable (can be hammered into sheets) and ductile (can be drawn into wires) because their structure consists of regular layers of ions. When a force is applied, these layers can slide over one another without breaking the metallic bond.

• Role of Electron Sea: The metallic bond is non-directional and flexible; as the ions slide, the 'sea' of delocalised electrons simply adjusts its shape. This prevents the repulsive forces between positive ions from causing the structure to shatter, which would occur in a brittle ionic crystal.

• Alloying Effects: While pure metals are often soft due to easy layer sliding, adding different sized atoms (alloys) can disrupt the regular arrangement. This 'locks' the layers in place, making the material significantly harder and less malleable.

• Comparison with Ionic Bonding: While both involve electrostatic attraction, metallic bonding involves delocalised electrons rather than the transfer of electrons between atoms. This allows metals to conduct electricity in the solid state, whereas ionic compounds only conduct when molten or dissolved.

• Precise Terminology: When explaining malleability, always use the terms 'ions' and 'layers'. Avoid using the word 'particles' as it is too vague; examiners specifically look for the mention of positive ions sliding over each other.

• Conductivity Logic: Always specify that it is the delocalised electrons that are free to move. Do not say 'atoms' or 'ions' are moving to conduct electricity, as the ions are fixed in their lattice positions in the solid state.

• Bonding Descriptions: Ensure you describe the attraction as 'electrostatic'. This term links the chemical concept to the physical force, which is essential for high-level marks in bonding questions.