The Reactivity Series: Unraveling the World of Chemical Reactivity

The reactivity series

Core Concepts

In this article, you will learn about the Reactivity Series, including its significance and its applications. After reading this article, you will be able to understand the nature of the Reactivity Series as well as its uses and functions.

Topics Covered in Other Articles

Defining the Reactivity Series

The reactivity series is a hierarchical arrangement of elements based on their relative tendency to undergo chemical reactions. It provides a systematic framework for comparing and ranking elements according to their reactivity. The series allows scientists to predict the behavior of elements when they come into contact with other substances and provides insights into the types of chemical reactions they are likely to undergo. Elements at the top of the reactivity series are the most reactive, while those at the bottom are the least reactive. This concept is essential in understanding various chemical phenomena, such as the extraction of metals, predicting reaction outcomes, and preventing corrosion.

Ordering the Reactivity Series

The reactivity series follows a general order, although slight variations can occur based on specific reaction conditions. Here is a commonly accepted order of elements in the reactivity series:

  1. Potassium
  2. Sodium
  3. Calcium
  4. Magnesium
  5. Aluminum
  6. Zinc
  7. Iron
  8. Lead
  9. Hydrogen
  10. Copper
  11. Silver
  12. Gold
  13. Platinum

It is important to note that this list provides a general guideline and may vary slightly depending on the specific reaction being considered.

Understanding Reactivity Trends

Alkali Metals and Alkaline Earth Metals

Alkali metals such as potassium, sodium, and calcium are all highly reactive elements. Because of their low ionization energies, they easily shed their outermost electrons, generating positive ions. The diminishing strength of the metallic link retaining the outermost electron enhances reactivity as we proceed down the group.

Transition Metals

Transition metals with moderate reactivity include iron and zinc. They may form compounds with a wide spectrum of elements and have numerous oxidation states. Because of their capacity to assist chemical processes without being consumed in the process, transition metals are frequently utilized as catalysts.

Noble Metals

Noble metals such as gold and platinum are distinguished by their low reactivity. They have stable electron configurations with entire or almost full outer electron shells, which makes them less reactive than other compounds. Because of their stability, noble metals may resist corrosion and stay in their pristine state in nature.

Significance of the Reactivity Series

Predicting and Balancing Reactions

The reactivity series can be used to forecast the results of chemical processes. Highly reactive components are more likely to react with other substances, whereas less reactive elements are less likely to react. Furthermore, by distinguishing the elements undergoing oxidation and reduction, the reactivity series aids in balancing redox equations.

Metallurgy and Extraction of Metals

The reactivity series is important in metallurgy, which is the science of recovering metals from their ores. Electrolysis is used to obtain highly reactive metals such as potassium and sodium. Copper and silver, on the other hand, may be extracted using less reactive procedures such as smelting and reduction.

Corrosion Prevention

Understanding the reactivity series is critical in the fight against corrosion. Knowing the relative reactivity of metals allows for the implementation of suitable protective measures. Sacrificial anodes comprised of highly reactive metals such as zinc, for example, are used to preserve iron or steel buildings against corrosion.

Practical Applications of the Reactivity Series

The reaction of Metals and Hydrogen with Water or Steam

ElementReaction with Water/Steam
potassiumReacts very violently to cold water
sodiumReacts violently to cold water
magnesiumReacts very slowly with water, but rapidly with steam
zincOnly reacts when powdered and heated strongly in steam
ironDoes not react with water, but reacts slowly with steam
hydrogenNo reaction
copperNo reaction with water or steam

Reaction with cold water

  • The more reactive metals will react with cold water to form metal hydroxide and hydrogen gas.
  • Potassium, sodium, and calcium all undergo reactions with cold water as they are the most reactive metals.

For Example, 

     \begin{gather*} {Ca + 2H_{2}O \rightarrow Ca\left(OH\right)_{2} + H_{2}} \\ {2K + 2H_{2}O \rightarrow 2KOH + H_{2}} \end{gather*}

Reaction with steam

Metals just below calcium in the reactivity series do not react with cold water but will react with steam to form a metal oxide and hydrogen gas. 

For example,

     \begin{gather*} {Mg + H_{2}O \rightarrow MgO + H_{2}} \end{gather*}

The reaction of metals and hydrogen with dilute (HCl) Acid

ElementReaction with dilute hydrochloric acid
potassiumVery violent – very explosive
sodiumVery violent – explosive
calciumVery rapid – lots of hydrogen gas produced
magnesiumRapid – bubbles of hydrogen produced steadily
zincSlow – bubbles of hydrogen produced slowly
ironSlow reaction – some bubbles produced
hydrogenNo reaction
copperNo reaction

Reaction with Dilute Acid

  • Only metals above hydrogen in the reactivity series will react with dilute acids
  • Unreactive metals below hydrogen, such as gold, silver, and copper, do not react with acids
  • The more reactive the metal then the more vigorous the reaction will be
  • Metals that are placed high on the reactivity series such as potassium and sodium are very dangerous and react explosively with acids
  • When acids react with metals, they form a salt and hydrogen gas

    The general equation is:

Metal + Acid → Salt + Hydrogen

Reaction with Oxygen

  • Some reactive metals, such as the alkali metals, react easily with oxygen
  • Silver, copper, and iron can also react with oxygen although much more slowly
  • When metals react with oxygen, a metal oxide is formed. 

    For example,

Metal + Oxygen → Metal Oxide

     \begin{gather*} {2Cu + O_{2} \rightarrow 2CuO} \end{gather*}

  • Oxygen has no effect on gold.

The reactivity series is a key concept in chemistry that explains elemental behavior and its role in chemical processes. It is a useful instrument in the area of chemical research, whether it’s anticipating reaction outcomes, understanding metal extraction methods, or implementing corrosion prevention measures.

Why does Iron corrode in the presence of Copper but not in the presence of Zinc?

AnswerOngoing from the bottom to the top of the series, the tendency to lose electrons increases, and hence, the oxidizing nature of metals increases.

Copper lies below Iron in the reactivity series, hence, Iron is a more oxidizable/ reactive metal than copper. Hence, iron corrodes in the presence of copper. While Zinc lies above Iron in the reactivity series and is more reactive than iron. Thus, in the presence of Zinc, iron does not corrode.

What happens when you place a Copper strip in a jar containing the MgSO4 solution?

AnswerSince Copper lies below magnesium in the reactivity series, it cannot replace magnesium from its salt solution. Hence, no change is observed when a Cu strip is placed in the MgSO4 solution.

Further Reading

More about metals

Interactive Periodic Table

More about Periodic Trends