The sea of electrons
In a metal, each atom lets go of its valence electrons. What is left behind are positive metal ions packed in neat rows, called a metallic lattice.
The released electrons are delocalised: they are free to move through the whole metal. We call them a sea of electrons.
The metallic bond is the attraction between the positive metal ions and the sea of delocalised electrons around them.
Explaining the properties of metals
| Property | Explanation |
|---|---|
| Conduct electricity | Delocalised electrons are free to move and carry charge through the metal |
| Conduct heat | Free electrons carry energy quickly from hot parts to cold parts |
| Malleable (can be hammered into sheets) and ductile (can be drawn into wires) | Layers of ions can slide over each other. The sea of electrons moves with them, so the bond is not broken |
| High melting and boiling points (most) | The attraction between ions and electrons is strong and acts in all directions |
| Shiny (lustrous) | Free electrons reflect light |
| High density (most) | Ions are packed very closely |
Alloys
An alloy is a mixture of a metal with at least one other element, usually another metal (or carbon).
Pure metals are often too soft, because their layers slide easily. In an alloy, atoms of different sizes sit among the metal ions and disrupt the layers, so they cannot slide as easily. The alloy is harder and stronger.
| Alloy | Made from | Used for |
|---|---|---|
| Steel | Iron + a little carbon | Buildings, bridges, cars |
| Stainless steel | Iron + chromium + nickel | Cutlery, sinks (does not rust) |
| Bronze | Copper + tin | Statues, medals |
| Brass | Copper + zinc | Door handles, musical instruments |
| Solder | Tin + other metals (traditionally lead) | Joining wires in electronics |
| 18 carat gold | Gold + copper and silver | Jewellery (pure gold is too soft) |
- Positive ions in a lattice
- Sea of delocalised electrons
- Attraction ions to electrons
- Conduct electricity and heat
- Malleable and ductile
- High melting point
- Shiny
- Mixture of metals
- Layers disrupted
- Harder, stronger
- Steel, bronze, brass
Quick summary
- A metallic bond is the attraction between positive metal ions and a sea of delocalised electrons.
- Free electrons explain conduction of electricity and heat, and the shine of metals.
- Layers of ions slide without breaking the bond, so metals are malleable and ductile.
- Alloys mix a metal with other elements. Different sized atoms stop layers sliding, so alloys are harder and stronger.
- Examples: steel (iron and carbon), bronze (copper and tin), brass (copper and zinc).
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