Metallic Bonding
Metallic bonding — the strong electrostatic attraction between a lattice of positive metal ions and the sea of delocalised electrons that surrounds them. Metal atoms lose their outer electrons, which become free to move throughout the entire metallic structure.
A regular lattice of positive metal ions sits in a ‘sea’ of delocalised electrons. Press a button to see how this structure explains a metal’s properties — each demonstration runs until you stop it.
Metallic bonding. Positive metal ions are arranged in a regular lattice, surrounded by a ‘sea’ of delocalised electrons that are free to move throughout the structure. The electrostatic attraction between the positive ions and the negative electron sea holds the metal together.
⇄ Why metals are malleable
The positive ions are arranged in layers. When a force is applied, the layers can slide over each other into new positions. This is why a metal can be bent and hammered into shape instead of shattering.
⚡ Why metals conduct electricity
Metals have delocalised electrons that are free to move through the whole structure. These electrons carry charge through the metal — this flow of electrons is the electric current.
🔥 Why metals conduct heat
The same delocalised electrons are free to move through the structure. They gain energy at the hot end and transfer this energy quickly to the cooler end.
Properties of Metals Explained by Metallic Bonding
| Property | Explanation |
|---|---|
| Conduct electricity | The delocalised electrons are free to move through the metal and carry charge, so they flow as an electric current. |
| Conduct heat | The delocalised electrons are free to move and transfer energy from the hot end to the cooler end. |
| Malleable and ductile (can be bent and shaped) | The layers of positive ions can slide over each other, so the metal can be hammered into shape (malleable) and drawn into wires (ductile). |
| High melting and boiling points | There are strong electrostatic attractions between the positive ions and the delocalised electrons. A large amount of energy is needed to overcome them, so most metals are solid at room temperature. |
| Shiny lustre | Delocalised electrons interact with light, reflecting it — giving metals their shiny appearance. |
Alloys
Alloy — a mixture of two or more elements where at least one is a metal. Common examples: steel (iron + carbon), brass (copper + zinc), bronze (copper + tin).
Pure metals have a regular arrangement of identical atoms. The layers of atoms can slide over each other easily, which makes pure metals soft and easy to deform.
In an alloy, atoms of a different element (with a different size) are introduced into the lattice. These different-sized atoms distort the regular layers, making it harder for them to slide over each other. This is why alloys are harder and stronger than the pure metals they are made from.
Two metal structures side by side — a pure metal and an alloy. Press the button to apply a force and watch whether the layers can slide over each other.
Why alloys are harder. Pure metal (left): identical ions in regular layers slide over each other easily. Alloy (right): atoms of a different size distort the layers, so they bump into each other and cannot slide — making the alloy harder and stronger.
Shape Memory Alloys (beyond the syllabus — useful context, not required knowledge)
Shape memory alloys can be deformed but then return to their original shape when heated. A well-known example is Nitinol (nickel–titanium alloy), used in dental braces — the alloy is bent to fit the teeth but slowly returns to its memorised shape as it warms to body temperature, gently straightening the teeth.
🧪 Exam-style questions
Iron is a metal. Describe how iron conducts thermal energy.
Show answer
The official AQA mark scheme awards 1 mark for each point:
- (Thermal) energy is transferred 1 mark (allow “heat is transferred”)
- by delocalised electrons 1 mark — the free electrons move through the structure, carrying energy from the hot end to the cooler end.
Pure iron is too soft for many uses.
Explain why mixing iron with other metals makes alloys which are harder than pure iron.
Show answer
The official AQA mark scheme awards 1 mark for each point:
- The alloy (mixture) contains different-sized atoms 1 mark
- (so the) layers are distorted 1 mark
- (so the) layers cannot easily slide over each other 1 mark (allow “atoms cannot slide over each other”)
Allow: “(positive / metal) ions” in place of “atoms” throughout.