Explaining the Reactivity Series

The reactivity series is a ranked list of metals (with carbon and hydrogen for comparison) showing how easily they lose electrons to form positive ions. It helps predict which reactions will happen.

Order to learn

Most reactive → least reactive: potassium (K), sodium (Na), calcium (Ca), magnesium (Mg), aluminium (Al), carbon (C), zinc (Zn), iron (Fe), hydrogen (H), copper (Cu), silver (Ag), gold (Au).

Why this order?

• More reactive metals lose electrons more easily (they form positive ions faster). This is oxidation.
• Example electron loss: $$\mathrm{Mg} \rightarrow \mathrm{Mg}^{2+} + 2e^-$$
• Apparent unreactivity of aluminium: it has a thin, tough oxide layer ($\mathrm{Al_2O_3}$) that stops water and air reaching the metal.

Evidence from reactions

• With water: K, Na, Ca react with cold water to make hydrogen gas and an alkaline solution; Mg reacts with steam; below Mg there is little/no reaction with water.
• With dilute acids: metals above hydrogen react to make hydrogen gas; metals below hydrogen do not react.
• Displacement: a more reactive metal displaces a less reactive metal from its compound in solution. $$\mathrm{Zn} + \mathrm{CuSO_4} \rightarrow \mathrm{ZnSO_4} + \mathrm{Cu}$$ Zinc displaces copper because Zn is above Cu.

Deducing the order

• If metal A displaces metal B from a solution, A is more reactive than B.
• Faster fizzing with acid or a greater temperature rise suggests higher reactivity.
• Use hydrogen and carbon as markers: above H → reacts with acids; above C → can be extracted only by electrolysis (not needed here, but explains the position of very reactive metals).

Common misconceptions

• “Aluminium is unreactive.” In fact, its oxide layer protects it; bare aluminium is reactive.
• “All metals react with acids.” Only those above hydrogen do.
• “A metal always displaces another.” Displacement happens only if the solid metal is higher in the series.