The reactivity of a metal is related to its tendency to form positive ions.

The idea

This statement links a metal's position in the reactivity series to how easily its atoms lose electrons and become positive ions. A reactive metal, such as potassium or calcium, loses its outer electrons readily and therefore forms positive ions easily. A less reactive metal, such as copper or gold, holds its electrons more strongly and forms positive ions only with difficulty. The greater the tendency to form positive ions, the more vigorously the metal reacts with water, acid or oxygen, and the more readily it displaces a less reactive metal from its compound. For example, zinc displaces copper from copper sulfate solution because zinc forms positive ions more readily than copper does. You should be able to use this idea to predict and explain trends in reactivity, rather than simply recalling a list.

What earns the marks

• Reactivity increases as the tendency of a metal to form positive ions increases.
• Metals that lose electrons readily form positive ions easily and are more reactive.
• Metals that form positive ions only with difficulty are less reactive.
• The tendency to form positive ions explains observed reactions with water, acid and oxygen.
• Displacement occurs when a more reactive metal, which forms positive ions more readily, takes the place of a less reactive metal in a compound.

Common mistakes and how to put them right

• Treating the reactivity series as an arbitrary list to memorise.

  Put it right by explaining each position in terms of how readily the metal forms positive ions.

• Saying that more reactive metals form negative ions.

  Put it right by stating that metals form positive ions, and reactivity relates to the ease of that formation.

• Assuming a less reactive metal cannot react at all.

  Put it right by saying it forms positive ions less readily, so reactions are slower or need more energy.

Exam tips

• When explaining a trend, use the phrase 'tendency to form positive ions' and link it to electron loss.
• Support predictions with a displacement example, naming the more reactive metal that forms ions more readily.
• Compare two named metals directly rather than describing reactivity in vague terms.