AQA · GCSE · Combined Science
Course version: 8464 · Version from Sept 2018
The electrons in the outer shell of metal atoms are delocalised and so are…
Full specification wording
Metallic bonding: The electrons in the outer shell of metal atoms are delocalised and so are free to move through the whole structure. The sharing of delocalised electrons gives rise to strong metallic bonds. The bonding in metals may be represented in the following form:
Metal atoms have few outer-shell electrons.
Checked against the AQA 8464 specification (opens in a new tab) on .
- Point 2 of 2
- 2 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
Metal atoms have few outer-shell electrons. In a giant metallic lattice, each metal atom releases these outer electrons into a shared pool. The electrons become delocalised: they are not attached to any one atom and can move throughout the whole structure. The positive metal ions remain in fixed positions, and the attraction between these ions and the delocalised electrons produces strong metallic bonds. This model explains why metals conduct electricity and heat, and why they have high melting points. For example, in sodium, each Na atom contributes one electron to the delocalised sea, forming Na⁺ ions. In magnesium, each Mg atom contributes two electrons, forming Mg²⁺ ions, so the bonding is stronger and the melting point is higher. Diagrams show positive ions in a regular arrangement surrounded by negative delocalised electrons.
What earns the marks
- Outer-shell electrons of metal atoms become delocalised, meaning they are not associated with any particular atom and are free to move through the entire metallic structure.
- The structure consists of positive metal ions arranged in a regular giant lattice, with delocalised electrons occupying the spaces between them.
- Metallic bonding arises from the strong electrostatic attraction between the positive metal ions and the shared delocalised electrons.
- The number of delocalised electrons per atom affects bond strength: magnesium contributes two electrons per atom, giving stronger metallic bonding and a higher melting point than sodium, which contributes one.
- Delocalised electrons can carry charge and kinetic energy through the metal, explaining why metals are good conductors of electricity and heat.
Common mistakes and how to put them right
Thinking that metal atoms share pairs of electrons in a covalent bond.
Put it right: In metallic bonding, outer electrons are delocalised and shared across the whole structure, not localised between two atoms.
Believing that the positive ions are free to move in a solid metal.
Put it right: The positive ions are fixed in a regular lattice; only the delocalised electrons move.
Stating that metallic bonds are weak because electrons are free.
Put it right: The attraction between the positive ions and the delocalised electrons is strong, which is why metals have high melting points.
Exam tips
- When drawing a metal lattice, show positive ions in a regular pattern and label the delocalised electrons clearly; include the charge on the ions, such as Na⁺ or Mg²⁺.
- Use the phrase 'delocalised electrons' rather than 'free electrons' to match the specification wording.
- Link the number of outer electrons per atom to the strength of metallic bonding when comparing metals such as sodium and magnesium.
Try the lesson
The start of the Metallic bonding: The electrons in the outer shell of metal atoms are delocalised and so are free to move through the whole structure. The sharing of delocalised electrons gives rise to strong metallic bonds. The bonding in metals may be represented in the following form: lesson, made from checked teaching notes for this specification point.
Have a go first
According to the model of metallic bonding, which statement correctly describes the electrons in the outer shell of metal atoms?
Listen
Metal atoms have few outer-shell electrons. In a giant metallic lattice, each metal atom releases these outer electrons into a shared pool. The electrons become delocalised: they are not attached to any one atom and can move throughout the whole structure. The positive metal ions remain in fixed positions, and the attraction between these ions and the delocalised electrons produces strong metallic bonds. This model explains why metals conduct electricity and heat, and why they have high melting points. For example, in sodium, each Na atom contributes one electron to the delocalised sea, forming Na⁺ ions. In magnesium, each Mg atom contributes two electrons, forming Mg²⁺ ions, so the bonding is stronger and the melting point is higher. Diagrams show positive ions in a regular arrangement surrounded by negative delocalised electrons. A strong answer earns marks for these points. Outer-shell electrons of metal atoms become delocalised, meaning they are not associated with any particular atom and are free to move through the entire metallic structure. The structure consists of positive metal ions arranged in a regular giant lattice, with delocalised electrons occupying the spaces between them. Metallic bonding arises from the strong electrostatic attraction between the positive metal ions and the shared delocalised electrons. The number of delocalised electrons per atom affects bond strength: magnesium contributes two electrons per atom, giving stronger metallic bonding and a higher melting point than sodium, which contributes one. A common slip: Thinking that metal atoms share pairs of electrons in a covalent bond. Instead, in metallic bonding, outer electrons are delocalised and shared across the whole structure, not localised between two atoms. Exam tip: When drawing a metal lattice, show positive ions in a regular pattern and label the delocalised electrons clearly; include the charge on the ions, such as Na⁺ or Mg²⁺.
Key words
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Metallic bonding model
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Delocalised electrons
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See every definition
- Metallic bonding model
- The bonding in metals may be represented by the sharing of delocalised electrons, which gives rise to strong metallic bonds.
- Delocalised electrons
- Outer-shell electrons of metal atoms that are not associated with any particular atom and are free to move through the entire metallic structure.
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