AQA · GCSE · Combined Science
Course version: 8464 · Version from Sept 2018
Chemical bonds: Metallic bonding occurs in metallic elements and alloys.
Metallic bonding explains why metals and alloys hold together and conduct.
- 4 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
Metallic bonding explains why metals and alloys hold together and conduct. In a pure metal such as magnesium, each atom contributes its outer electrons to a delocalised sea that surrounds a regular lattice of positive ions. The attraction between the positive ions and the shared negative electrons is the metallic bond, acting in all directions rather than between specific pairs. Alloys such as steel or bronze contain atoms of different sizes, which disrupt the regular layers so they cannot slide as easily, making the alloy harder. This model accounts for the high melting points, malleability and electrical conductivity of metallic substances, and it applies to metallic elements and to alloys alike.
What earns the marks
- Metallic bonding is the electrostatic attraction between positive metal ions and delocalised electrons.
- The structure is a giant lattice of positive ions in a sea of delocalised electrons.
- The bonding acts in all directions and is not directional between particular pairs of atoms.
- Outer-shell electrons are delocalised, so they are free to move through the lattice.
- Alloys contain atoms of different sizes, which distort the regular layers and make sliding harder.
- The model explains properties such as conductivity, malleability and high melting points.
Common mistakes and how to put them right
Saying metallic bonding is between positive and negative ions.
Put it right by stating it is between positive ions and delocalised electrons.
Describing delocalised electrons as belonging to one particular atom.
Put it right by saying they are shared across the whole lattice.
Claiming alloys are weaker because different-sized atoms break the bonds.
Put it right by explaining that different-sized atoms disrupt the regular layers so they cannot slide, making the alloy harder.
Exam tips
- Use the phrase 'electrostatic attraction between positive ions and delocalised electrons' when explaining metallic bonding.
- Link each property you describe back to the model, for example free electrons explain conductivity.
- When comparing an alloy with a pure metal, refer to the sizes of the atoms and the effect on sliding layers.
Try the lesson
The start of the Chemical bonds: Metallic bonding occurs in metallic elements and alloys. lesson, made from checked teaching notes for this specification point.
Have a go first
Which type of bonding is found in a piece of pure copper metal?
Key words
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Electrostatic attraction
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Delocalised electrons
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Giant lattice structure
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Structure and properties of alloys
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See every definition
- Electrostatic attraction
- The force between positive metal ions and delocalised electrons, which is the metallic bond.
- Delocalised electrons
- Outer-shell electrons that are shared across the whole lattice and are free to move through it.
- Giant lattice structure
- A regular arrangement of positive ions surrounded by a sea of delocalised electrons.
- Structure and properties of alloys
- Atoms of different sizes distort the regular layers so they cannot slide as easily, making the alloy harder.
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