The reactivity series: When metals react with other substances the metal atoms form positive ions. The reactivity of a metal is related to its tendency to form positive ions. Metals can be arranged in order of their reactivity in a reactivity series. The metals potassium, sodium, lithium, calcium, magnesium, zinc, iron and copper can be put in order of their reactivity from their reactions with water and dilute acids.

The idea

Metal atoms lose electrons to form positive ions, for example Na → Na⁺ + e⁻ and Mg → Mg²⁺ + 2e⁻. The more readily a metal forms positive ions, the more reactive it is. Reactivity is therefore linked to the tendency to form positive ions, not to density, hardness or melting point. The reactivity series places metals in order, with potassium, sodium, lithium, calcium, magnesium, zinc, iron and copper from most to least reactive among those listed. The order is established by observing reactions with water and dilute acids: potassium reacts violently with cold water, sodium and lithium react vigorously, calcium reacts steadily, magnesium reacts very slowly with cold water but rapidly with dilute acid, zinc and iron react more slowly with acid, and copper does not react with water or dilute acid.

What earns the marks

• Metal atoms form positive ions by losing electrons, for example Na → Na⁺ + e⁻ and Ca → Ca²⁺ + 2e⁻.
• The reactivity of a metal is related to its tendency to form positive ions; a greater tendency means greater reactivity.
• The reactivity series orders metals from most reactive to least reactive, and the listed order is potassium, sodium, lithium, calcium, magnesium, zinc, iron, copper.
• Reactions with cold water and dilute acids provide the evidence used to place metals in the series.
• Potassium, sodium and lithium react vigorously with cold water, while copper shows no reaction with water or dilute acid.
• Magnesium reacts very slowly with cold water but reacts readily with dilute acid, so the two tests can give different apparent rates.
• Observations such as fizzing, metal dissolving, temperature rise and gas produced are used to compare reactivity.

Common mistakes and how to put them right

• Writing ion symbols without charge, such as Na or Mg, instead of Na⁺ and Mg²⁺.

  Put it right: The positive charge is the key feature of the ion formed.

• Placing copper above iron in the series because copper is familiar or used in wires.

  Put it right: Copper is less reactive than iron and does not react with dilute acid.

• Assuming that a more reactive metal must be denser or harder.

  Put it right: Reactivity depends on the tendency to form positive ions, not on physical properties.

• Saying that magnesium 'does not react with water' without qualification.

  Put it right: It reacts very slowly with cold water, so state the condition and the acid result separately.

Exam tips

• Learn the listed order as a sequence and practise writing it from most to least reactive without prompts.
• When comparing two metals, quote a specific observation such as rate of fizzing or temperature change rather than saying one is 'more reactive' with no evidence.
• Link each reactivity statement back to positive ion formation, for example 'potassium is more reactive because it forms K⁺ more readily than iron forms Fe²⁺'.
• Check that any ion you write has the correct charge, such as 1⁺ for Na⁺ and 2⁺ for Mg²⁺.