Reactivity of metals

Chemistry · Chemical changes. The idea in plain words, the rules to remember, the mistake to avoid and a worked example, written and checked by Mega Lecture.

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The idea

Metals react by losing electrons to form positive ions. The more easily a metal does this, the more reactive it is. The reactivity series puts metals in order, found by seeing how fast each one reacts with water and with dilute acids.

A more reactive metal pushes a less reactive metal out of its compound. This is a displacement reaction. Carbon can do the same job: it takes the oxygen from the oxides of metals below it, which is how zinc and iron are extracted.

Gaining oxygen is oxidation and losing oxygen is reduction. In terms of electrons, losing electrons is oxidation and gaining electrons is reduction.

Rules to remember

Order, most reactive first: potassium, sodium, lithium, calcium, magnesium, (carbon), zinc, iron, (hydrogen), copper, gold
Oxidation = gain of oxygen; reduction = loss of oxygen
Oxidation is loss of electrons, reduction is gain of electrons (OIL RIG)
A more reactive metal displaces a less reactive metal from its compound
Metals less reactive than carbon are extracted by heating the oxide with carbon
Gold is so unreactive that it is found in the Earth as the metal itself
Ionic equations leave out the ions that do not change (spectator ions)

Common mistake

Students say the metal atom is reduced because it 'gets smaller' or the ion is oxidised. Look at the electrons: the metal atom that becomes an ion loses electrons, so it is oxidised.

Worked example

Zinc is added to silver nitrate solution. Zinc is more reactive than silver. Write the ionic equation and say what is oxidised and what is reduced.

Zinc is more reactive, so it displaces silver from the solution.
Zinc atoms form Zn²⁺ ions and silver ions, Ag⁺, form silver atoms. Nitrate ions do not change, so leave them out.
Balance the charge: one Zn loses 2 electrons, so two Ag⁺ ions are needed: Zn + 2Ag⁺ → Zn²⁺ + 2Ag.
Zinc loses electrons, so it is oxidised. Silver ions gain electrons, so they are reduced.

Answer: Zn + 2Ag⁺ → Zn²⁺ + 2Ag. Zinc is oxidised and silver ions are reduced.

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