Metallic bonding (AQA GCSE Chemistry Combined Science): Revision Notes
Metallic bonding
What is metallic bonding?
Understanding Metallic Bonding
Metallic bonding is the unique way that metal atoms join together, creating the distinctive properties we associate with metals.
Metallic bonding happens in metals and alloys. When metal atoms come together, their outer electrons become delocalised. This means the electrons can move freely around the whole structure.
The delocalised electrons leave behind positive metal ions. These metal ions arrange themselves in a regular pattern called a lattice.
How metallic bonding works
The process of metallic bonding can be understood by examining what happens at the atomic level when metals form their characteristic structures.
Worked Example: Sodium Metal Formation
Let's look at sodium as an example:
- Each sodium atom loses its outer electron
- This creates positive sodium ions (Na⁺)
- The lost electrons form a "sea of electrons" that can move freely
- The electrons don't belong to any particular atom - they belong to the whole structure
The strong electrical pull between the positive metal ions and the negative delocalised electrons creates the metallic bond. This attraction holds the metal together.
Structure of metals
Metals have a very organised structure that gives them their unique properties:
- Metal ions are arranged in a regular pattern
- Delocalised electrons move freely throughout the whole structure
- The electrons act like glue, holding the metal ions in place
The ability of electrons to move freely throughout the metal structure is what gives metals their excellent electrical conductivity and other characteristic properties.
Properties of metals and alloys
Understanding why metals behave as they do requires looking at both pure metals and their mixtures.
Pure metals
- Large amounts of metals like copper, gold, iron and aluminium are used every day
- Pure metals are often too soft for many jobs
- That's why we mix metals together to make alloys
Alloys
- Alloys are mixtures of different metals
- They are much harder than pure metals
- This makes them more useful for practical applications
Why Alloys Are Important
The mixing of different metals disrupts the regular arrangement of atoms, making it harder for layers to slide over each other. This is what makes alloys stronger and more durable than pure metals.
Practical examples
Real-world applications demonstrate how the properties of metallic bonding make metals useful for specific purposes.
Worked Example: Solder Applications
Solder is an alloy made from tin and lead. It's perfect for joining electrical components because:
- It melts at a low temperature (183°C)
- It conducts electricity well
- It's not too hot, so it won't damage delicate electrical parts
Worked Example: Copper Cooking Pans
Copper is used to make cooking pans because:
- It has a high melting point (1085°C) so it can get very hot
- It conducts heat well for even cooking
Sodium and magnesium have much lower melting points (98°C and 649°C), so they would melt and be dangerous for cooking.
Key Points to Remember:
- Metallic bonding happens when metal atoms lose their outer electrons to form a "sea of electrons"
- The delocalised electrons can move freely around the whole metal structure
- Metal ions are held together by the electrical pull from the delocalised electrons
- Alloys are mixtures of metals that are harder than pure metals
- Different metals have different melting points and electrical conductivity, making them useful for different jobs