The reactivity series and oxidation/reduction (in terms of oxygen)
Metals react with oxygen, water and acids at very different speeds. The order from most to least reactive is the reactivity series — one of the most useful tables in GCSE Chemistry. It explains why iron rusts but gold doesn't, why sodium is stored under oil, and why carbon can extract iron but not aluminium.
The reactivity series (must memorise)
From most → least reactive:
Potassium → Sodium → Lithium → Calcium → Magnesium → (Carbon) → Zinc → Iron → (Hydrogen) → Copper → Silver → Gold
Mnemonic: "Please Send Lions, Cats, Monkeys (and Carbon) Zebras In Hot Continents Sometimes Gold."
Carbon and hydrogen are non-metals included for comparison: any metal below carbon can be extracted by reduction with carbon (C4.2); any metal below hydrogen does not displace hydrogen from acids.
Reactions with water
- K, Na, Li, Ca: react with cold water → metal hydroxide + hydrogen. Example: 2Na + 2H₂O → 2NaOH + H₂.
- Mg: very slow with cold water; reacts with steam → MgO + H₂.
- Zn, Fe: react with steam.
- Cu: no reaction even with steam.
Reactions with acids
Metals above hydrogen in the series react with dilute acids: metal + acid → salt + hydrogen
Example: Mg + 2HCl → MgCl₂ + H₂. Bubbles of hydrogen are seen; the metal is consumed; the temperature usually rises slightly. The more reactive the metal, the faster the bubbles.
Copper, silver and gold do not react with dilute acids.
Oxidation and reduction in terms of oxygen
At GCSE Foundation, redox is defined by oxygen:
- Oxidation = gain of oxygen.
- Reduction = loss of oxygen.
Mnemonic: "OIL RIG" (Oxidation Is Loss [of electrons], Reduction Is Gain — see C4.3 for HT extension).
When magnesium burns: 2Mg + O₂ → 2MgO
- Mg gains oxygen → magnesium is oxidised.
- O₂ loses to form an oxide of Mg — overall O is captured (the reducing agent here is Mg itself).
When iron oxide reacts with carbon in a blast furnace: 2Fe₂O₃ + 3C → 4Fe + 3CO₂
- Fe₂O₃ loses oxygen → iron oxide is reduced.
- C gains oxygen → carbon is oxidised.
Why reactivity differs
A more reactive metal more readily loses electrons to form positive ions. Sodium loses 1 electron easily (low ionisation energy); copper holds its electrons more tightly. The ease of electron loss controls how vigorously a metal reacts.
⚠Common mistakes
- Forgetting carbon's position, then thinking it can extract aluminium (it can't — Al is above C).
- Saying "metal + acid → salt + water" (that's metal oxide + acid). Correct for metal + acid: salt + hydrogen.
- Mixing oxidation/reduction definitions. In O₂ context: oxidation = gain O; reduction = lose O.
- Saying gold reacts slowly — gold doesn't react with water or acids at all in GCSE conditions.
Links
Sets up C4.2 (extraction with carbon), C4.3 (redox in terms of electrons HT), C4.4 (acid + metal). Reactivity series explains C10.7 corrosion and C10.8 alloy choices.
AI-generated · claude-opus-4-7 · v3-deep-chemistry