Metals have a tendency to lose electrons. The tendency to lose electrons differs from one metal to another and this can be arranged in the form of a series. The arrangement of metals in the decreasing order of their reactivity is called the activity series of metals or the reactivity series. The metal potassium (most reactive) is kept at the top and gold is kept at the bottom (least reactive). Hydrogen is a non-metal but still, it is included in the series because it can form positive ions. The following is the reactivity series of metals:
Salient features of the reactivity series:
- While moving down the reactivity series the electropositive character decreases. Potassium and sodium react with oxygen to form superoxide but in the limited supply of oxygen, they form their own oxides.
K + O2 –> KO2
- On moving down the reactivity series the reducing power of metals decreases. Hence potassium is the strongest reducing agent.
- Metals have a tendency to lose electrons and get oxidized. This tendency of getting oxidized decreases as we move down the activity series. Therefore potassium gets oxidized most readily.
- The ability of metals to reduce water into hydrogen reduces as we move down the reactivity series. Potassium and sodium being highly reactive, react with cold water to liberate hydrogen gas which gets ignited by the heat produced in the reaction.
2K + 2H2O –> 2KOH + H2 ↑
- All the metals which are placed above hydrogen in the activity series have the ability to reduce hydrogen ions from dilute hydrochloric or dilute sulphuric acid to liberate hydrogen gas.
- A metal which is placed higher in the reactivity series can replace a metal below it in order to form the salt solutions of the latter metal. If the difference between the positions of two metals is very large then the displacement reaction will be very rapid.
- The oxides of metals like potassium, sodium, calcium, magnesium, and aluminum cannot be reduced by the common reducing agents.
Reactions with acids and water
Metal hydroxides and hydrogen will be produced when a highly reactive metal like Na reacts with cold water
2 Na (s) + 2 H2O (l) →2 NaOH (aq) + H2 (g)
Metal salts such as Iron sulfate and hydrogen will be produced when a metal that’s at the middle of the reactivity series, in this instance Fe (Iron), reacts with acids here, H2SO4.
Fe (s) + H2SO4 (l) → FeSO4 (aq) + H2 (g)
Obviously some exceptions exist such as Mg (Magnesium), Al (Aluminum), and Zn (Zinc) that can react with H2O. But as the reaction goes on it also slows down considerably as the oxides formed on the surface of the metal protects it.
Single Displacement Reaction
The iron will be transformed into its sulfate when an iron nail is dropped in a copper sulfate solution leaving behind copper i.e. a metal.
Fe (s) + CuSO4 (aq) → Cu (s) + FeSO4 (aq)
The metals higher in the reactivity series will replace any metals lower than them because the lower metals ions are reduced by the higher metals. Kroll process and thermite reaction are two instances where this concept is used. Aluminium oxide and Iron will be produced when Aluminium reacts with Fe2O3 reducing it down to the above-mentioned products.
Al (s) + Fe2O3 (s) → Fe (s) + Al2O3 (s)
We have seen the significant properties of the reactivity series and the order of metals placed in it. For any further details install Byju’s the learning app and explore the world of education.