Metals

The One Thing

Metallic structure explains the characteristic properties of metals, while the reactivity series predicts their reactions and determines how they are extracted. Alloys modify metallic properties, and corrosion can be controlled by preventing or redirecting oxidation.

Reactions, Processes and Experiments

Key Terms

• Metallic bonding: The strong electrostatic attraction between a lattice of positive metal ions and a sea of delocalised electrons.
• Delocalised electrons: Electrons free to move through the metal structure, allowing metals to conduct electricity and heat.
• Malleable: Able to be hammered or pressed into different shapes without breaking.
• Ductile: Able to be drawn into wires.
• Reactivity series: An arrangement of metals from most reactive to least reactive, often including potassium, sodium, lithium, calcium, magnesium, aluminium, carbon, zinc, iron, hydrogen, copper, silver and gold.
• Displacement reaction: A reaction in which a more reactive metal replaces a less reactive metal from its compound.
• Ore: A naturally occurring rock containing enough of a metal compound for the metal to be extracted economically.
• Extraction: The process of obtaining a metal from its ore.
• Reduction: Removal of oxygen from a compound or gain of electrons.
• Oxidation: Addition of oxygen to a substance or loss of electrons.
• Electrolysis: Decomposition of an ionic compound using electricity when the compound is molten or dissolved.
• Alloy: A mixture of a metal with one or more other elements, designed to improve properties.
• Corrosion: The gradual destruction of a metal by chemical reactions with substances in its environment.
• Rusting: Corrosion of iron or steel in the presence of oxygen and water, producing hydrated iron(III) oxide.
• Passivation: Formation of a thin protective oxide layer that prevents further reaction, as occurs with aluminium.

Easily Confused

• Reduction and oxidation: Reduction is removal of oxygen or gain of electrons; oxidation is addition of oxygen or loss of electrons.
• Rusting and corrosion: Rusting is the corrosion specifically of iron or steel in oxygen and water; corrosion is the broader process affecting metals.
• Galvanising and sacrificial protection: Galvanising coats iron or steel with zinc, which provides a barrier and may also oxidise sacrificially; sacrificial protection connects iron to a more reactive metal, such as magnesium or zinc.
• Extraction and purification: Extraction obtains a metal from its ore; purification removes impurities from an already extracted metal, as in electrolytic purification of copper.
• Electrolysis and reduction with carbon: Electrolysis is required for metals more reactive than carbon, such as aluminium; metals less reactive than carbon can often be extracted by heating their oxides with carbon.
• Steel and stainless steel: Steel is mainly iron and carbon; stainless steel contains iron, chromium and often nickel.
• Brass and bronze: Brass is copper and zinc; bronze is copper and tin.
• Malleability and ductility: Malleability concerns being shaped by hammering or pressing; ductility concerns being drawn into wires.
• Cold-water and steam reactions of magnesium: Magnesium reacts slowly with cold water but more readily with steam.
• Protective coating and passivation: A protective coating is applied externally, whereas passivation is the formation of a thin protective oxide layer, as occurs naturally with aluminium.

What Gets Asked

• Explain how metallic bonding accounts for conductivity, high melting points, strength, malleability and ductility. The mark-losing error is omitting the mobile delocalised electrons or the strong attraction between positive metal ions and those electrons.
• Use the reactivity series to predict a displacement reaction, such as Zn + CuSO4 -> ZnSO4 + Cu. The key error is predicting displacement when the reacting metal is not higher in the reactivity series.
• Predict whether a metal reacts with dilute acid or water. Metals above hydrogen generally produce hydrogen with dilute acids, whereas copper does not usually do so; potassium, sodium and lithium react very vigorously with cold water, while magnesium reacts more readily with steam.
• Select an extraction method from a metal’s position relative to carbon. Very unreactive metals such as gold may occur uncombined, metals less reactive than carbon can often be reduced with carbon, and metals more reactive than carbon, such as aluminium, require electrolysis.
• Complete or interpret extraction equations, including 2CuO + C -> 2Cu + CO2, Fe2O3 + 3CO -> 2Fe + 3CO2, and the blast-furnace reactions involving coke and limestone. A common error is confusing carbon monoxide with carbon as the reducing agent in iron extraction.
• Describe corrosion prevention or electrolytic purification. The specific distinctions are that rusting requires both oxygen and water, salt accelerates rusting, zinc or magnesium can act sacrificially, and in copper purification copper is reduced at the cathode and oxidised at the anode.