Metallic Bonding

Introduction to Metallic Bonding

Metallic Bonding: Electrostatic attraction that occurs between a lattice of positive metal ions and delocalised electrons. These electrons move freely among atoms and are not confined to any specific atom.

Metals exhibit distinctive properties such as high electrical conductivity, malleability, and ductility due to this bonding mechanism.

Types of Chemical Bonding

• Ionic Bonding: Involves electron transfer resulting in charged ions. Example: Formation of sodium chloride.
• Covalent Bonding: Characterised by electron sharing between atoms. Example: Creation of water molecules.
• Metallic Bonding: Features delocalised electrons that facilitate non-directional interactions. Example: Metals such as copper.

Core Concept of Metallic Bonding

Metallic bonding is a distinct form of chemical bonding characterised by delocalised electrons. Picture marbles on a vibrating dance floor as a model for the movement within the metal lattice.

Properties of Metals

Metals display specific properties as a result of metallic bonding:

• Malleability: The ability to be hammered into thin sheets.
• Ductility: The capacity to be drawn into wires.
• Electrical Conductivity: Efficient conduction of electricity.
• Thermal Conductivity: Effective heat conduction.
• Lustre: Shiny appearance due to light reflecting off delocalised electrons.

Detailed Explanations

Malleability and Ductility

• Malleability: Capability of being hammered into sheets without fracturing.
• Ductility: Capacity to be stretched into wires without breaking. These properties are crucial in metalworking and various industrial applications.
• Mechanism: The 'sea of electrons' allows metal ions to move past one another, maintaining structural integrity, akin to layers of balls sliding over springs.

Electrical Conductivity

• Electron Sea Model: Delocalised electrons facilitate electrical conductivity.
• Process:
  • Electrons are free to move.
  • An external electric field causes electron flow.
  • Current flows readily through the metal.

Thermal Conductivity

• Energy Transfer: Vibrating ions and free electrons enable effective heat conduction.

Lustre

• Shiny Appearance: Metals appear shiny as light reflects off the electron clouds.

Visualising Metallic Structures

• Ball-and-Stick Models: Used to visualise metal lattices and electron seas.

Real-World Analogies

• Flow of Electricity: Comparable to water moving through pipes, illustrating easy electron mobility.
• Structural Flexibility: Similar to how aluminium foil bends, metals display flexibility in practical applications.

Metallic Structure and Bonding Theories

Detailed Explanation of Metallic Lattice

• Metallic Lattice Overview: Consists of orderly, repeating patterns of metal atoms.
• Types of Arrangement:
  • Face-Centred Cubic (FCC): Offers high ductility and good conductivity (e.g., Aluminium).
  • Body-Centred Cubic (BCC): Known for high strength (e.g., Iron).
  • Hexagonal Close-Packed (HCP): Provides strength and is lightweight (e.g., Titanium).

Lattice Type	Properties	Example Metals	Applications
FCC	High ductility, Good conductivity	Aluminium	Power lines, Kitchen utensils
BCC	High strength	Iron	Structural beams
HCP	Strength, Lightweight	Titanium	Aerospace components

Electron Sea Model

• Theory Description: Proposes a 'sea' of electrons that accounts for malleability and conductivity.

Factors Affecting Metallic Bonding

Key Considerations

• Type of Metal: Transition metals possess stronger bonds due to d-orbitals.
• Delocalised Electrons: An increased number of electrons strengthens bonds.
• Size of Metal Ions: Smaller ions allow denser packing and stronger bonds.

External Conditions

• Temperature and Pressure: Influence electron positioning and the strength of bonds.

Exam Preparation

Common Exam Questions

• Describe Metallic Bonding: Involves delocalised electrons that enable both conductivity and malleability.
• Structure Determination: Evaluate metals' lattice structures and their impact on properties.

Worked Example: Understanding Metallic Properties

Question: Explain why copper is an excellent conductor of electricity.

Solution:

1. Copper atoms in a metallic lattice each contribute one electron to the delocalised "electron sea"
2. These delocalised electrons are free to move throughout the lattice
3. When a potential difference is applied, these electrons flow as an electric current
4. Copper has a particularly high number of free electrons per atom, making it an exceptional conductor

Question: Why does aluminium's melting point (660°C) differ from iron's melting point (1538°C)?

Solution:

1. Iron has a stronger metallic bond than aluminium
2. Iron atoms contribute more delocalised electrons to the electron sea
3. Iron's electron configuration includes d-orbital electrons, creating stronger bonds
4. The stronger metallic bonds in iron require more thermal energy to overcome
5. Therefore, iron has a significantly higher melting point than aluminium