AQA Chemistry 5.2.1.5 · Model
Metallic bonding
One picture of a metal explains why a copper wire carries current, a pan handle gets hot and gold can be beaten thinner than paper. What is that picture?
Combined Science · Foundation tier
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A grain of gold, hammered into a sheet the size of a tablecloth.
Gold-beaters hammer one gram of gold into a sheet close to a square metre in area, only a few hundred atoms thick. It never cracks. Hit a grain of salt, another giant structure of charged particles, and it shatters at the first blow.
Commit first
What must be true inside gold for it to bend instead of break?
In a metal, every atom gives up its outer electrons. Those electrons do not belong to any one atom any more: they are delocalised, free to move through the whole structure. What is left behind is a regular lattice of positive metal ions, sitting in a sea of delocalised electrons. The metallic bond is the strong electrostatic attraction between the positive ions and that sea. Before you test the model, check you have the bond in the right place.
Think again
“In a metal, each atom is bonded to the atoms next to it.”
Spot the flaw
DescribeWhat is wrong with that description?
The electron-sea workbench
One model. Three experiments. Call each one first.
0 of 3 experiments
Metal ions (+) in a sea of delocalised electrons (dots)
Commit first. When the battery is connected, what moves through the solid metal?
Link property to model
Which part of the model explains it?
Six properties of metals. Each one comes from one feature of the electron-sea model.
Tap a card, then tap the box it belongs in. Tap a placed card to take it back.
Command words in this lesson
- Describe
- Give the model: positive ions, delocalised electrons, the attraction between them.
- Explain
- Property, then the feature of the model that causes it.
- Suggest
- Apply the model to a use you have not been taught.
Key fact
A metal is a lattice of positive ions in a sea of delocalised electrons. The metallic bond is the strong attraction between the ions and the electrons, not between atoms.
Examiner tip
Key note · AQA 5.2.1.5
Metallic bonding
- Metals are giant structures of positive ions in a regular lattice.
- The outer electrons are delocalised: free to move through the whole metal.
- The metallic bond is the strong electrostatic attraction between the positive ions and the delocalised electrons.
- Conduct electricity and heat, even as solids: the delocalised electrons move and carry charge and energy.
- Malleable and ductile: layers of ions slide, and the electron sea keeps holding them.
- High melting points: a lot of energy is needed to overcome the strong attraction.
Photograph this card. Tomorrow, cover it and say each line first.
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Mixing up the metallic bond with an ionic one?
The workbench is a two-dimensional model of a metal lattice with one delocalised electron per ion. In the battery view the electron drift is hugely speeded up so that it can be seen; real drift speeds are fractions of a millimetre per second. In the heat view, energy is shown spreading by stronger vibration of the ions and faster electrons.