2.4 Metallic bonding and the properties of metals
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Which statement describes metallic bonding?
Choose one answer.
Correct Not quite: the answer is Positive ions are attracted to delocalised electrons
Mark scheme
B
Model answer
B: positive metal ions are attracted to the sea of delocalised electrons.
Explain why metals conduct electricity.
Mark scheme
- metals contain delocalised electrons (1)
- which can move through the structure and carry charge (1)
Model answer
Metals contain delocalised electrons that are free to move through the structure, carrying electric charge.
Explain why pure metals can be hammered into shape (are malleable).
Mark scheme
- the layers of atoms / ions can slide over each other (1)
- the metallic bonding still holds them together / is not broken (1)
Model answer
The layers of ions slide over each other when a force is applied, but the delocalised electrons still hold them together.
Brass is an alloy of copper and zinc. Explain why brass is harder than pure copper.
Mark scheme
- zinc atoms are a different size from copper atoms (1)
- which distorts the layers (1)
- so the layers cannot slide over each other as easily (1)
Model answer
Zinc atoms are a different size to copper atoms, so they distort the regular layers. The layers can no longer slide over each other easily, making brass harder.
Explain why metals usually have high melting points.
Mark scheme
- strong electrostatic attraction between the positive ions and the delocalised electrons (1)
- a lot of energy is needed to overcome it (1)
Model answer
The metallic bonds between positive ions and delocalised electrons are strong, so a lot of energy is needed to overcome them.
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