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Transition metals, alloys and corrosion
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Transition metals are strong, useful and often colourful. Alloys and rust prevention make metals even more useful. Separate Chemistry only.
Transition metals
Found in the centre of the periodic table: iron, copper, nickel, chromium.
They have high melting points and high densities, form coloured compounds, and are often catalysts (iron in the Haber process).
They have high melting points and high densities, form coloured compounds, and are often catalysts (iron in the Haber process).
Alloys
An alloy is a mixture of a metal with other elements. Different-sized atoms disrupt the layers, so they cannot slide as easily: alloys are harder than pure metals.
Steel (iron and carbon), brass (copper and zinc), bronze (copper and tin), 18-carat gold (gold with copper or silver).
Steel (iron and carbon), brass (copper and zinc), bronze (copper and tin), 18-carat gold (gold with copper or silver).
Corrosion
Rusting needs both oxygen and water.
Prevented by barriers (paint, oil, plastic), galvanising (zinc coating) or sacrificial protection (a more reactive metal corrodes instead).
Prevented by barriers (paint, oil, plastic), galvanising (zinc coating) or sacrificial protection (a more reactive metal corrodes instead).
Why is a zinc coating on iron still protective even when scratched?
- Zinc is more reactive than iron.
- Zinc oxidises instead of the iron.
- This is sacrificial protection.
Answer: Zinc corrodes instead of the iron.
Transition metals: high melting points and densities, coloured compounds, catalysts. Alloys are harder because different atoms stop layers sliding. Rusting needs oxygen and water; prevent with barriers or sacrificial metals.
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