The Reactivity Series

Definition and Purpose

The reactivity series is a list of metals arranged in order of their reactivity, from the most reactive at the top to the least reactive at the bottom. It helps predict how metals will react with other substances, such as water and acids, and whether one metal can displace another from a compound.

This series is also essential for understanding how metals are extracted from their ores. More reactive metals require more energy-intensive methods, while less reactive metals can be extracted more easily.

Common Metals in the Series

The reactivity series includes many metals, but the most commonly studied ones in GCSE are:

• Very reactive metals: Potassium (K), Sodium (Na), Calcium (Ca)
• Moderately reactive metals: Magnesium (Mg), Aluminium (Al)
• Less reactive metals: Zinc (Zn), Iron (Fe)
• Least reactive metals: Copper (Cu), Silver (Ag), Gold (Au)

These metals are arranged in order of their tendency to lose electrons and form positive ions.

Reactivity Trends

Reactivity decreases as you move down the series. This means metals at the top, like potassium and sodium, react very vigorously, while metals at the bottom, like gold and silver, are very unreactive.

More reactive metals lose electrons more easily to form positive ions. This is why they react more readily with water and acids:

• Very reactive metals like potassium and sodium react explosively with water.
• Moderately reactive metals like magnesium react slowly with cold water but faster with steam.
• Less reactive metals like zinc and iron react with acids but not with water.
• Least reactive metals like copper do not react with water or dilute acids easily.

For example, potassium reacts with water to produce potassium hydroxide and hydrogen gas:

$\text{2K} + 2\text{H}_2\text{O} \rightarrow 2\text{KOH} + \text{H}_2$

For instance, magnesium reacts slowly with cold water but more quickly with steam to form magnesium oxide and hydrogen:

$\text{Mg} + \text{H}_2\text{O (steam)} \rightarrow \text{MgO} + \text{H}_2$

Displacement Reactions

A displacement reaction occurs when a more reactive metal displaces a less reactive metal from a compound, usually a salt solution. This is a key way to identify the relative reactivity of metals.

This happens because the more reactive metal loses electrons more easily and forms positive ions, while the less reactive metal gains electrons and forms solid metal.

For example, zinc is more reactive than copper, so zinc will displace copper from copper sulfate solution:

$\text{Zn} + \text{CuSO}_4 \rightarrow \text{ZnSO}_4 + \text{Cu}$

Here, zinc atoms lose electrons and go into solution as zinc ions, while copper ions gain electrons and form copper metal.

This principle is used in metal extraction and purification processes.

Example: If iron is placed in a solution of copper sulfate, iron will displace copper because iron is more reactive:

$\text{Fe} + \text{CuSO}_4 \rightarrow \text{FeSO}_4 + \text{Cu}$