7.5.1 Reactivity Series

Introduction

Metals can be arranged into a reactivity series based on their observed reactions with acids, cold water, and steam.

The reactivity series helps us understand:

• Which metals are more reactive and which are less reactive.
• How metals behave in different reactions.
• Which metals can displace others from their compounds.

This section explains the reactivity series and groups metals into four categories based on their reactivity.

Definition

Reactivity Series: The reactivity series is an arrangement of metals in order of their decreasing reactivity with acids, cold water, and steam.

In simple words: The reactivity series is a list of metals from most reactive to least reactive.

Main Idea

Metals can be arranged into a reactivity series based on their observed reactions with acids, cold water, and steam. Metals can be grouped into four groups:

• Highly Reactive Metals — react vigorously with cold water, steam, and acids.
• Moderately Reactive Metals — react slowly or not at all with cold water; react with steam and acids.
• Less Reactive Metals — do not react with cold water or steam; react slowly or not at all with acids.
• Unreactive Metals — do not react with cold water, steam, or acids under normal conditions.

Simplified Reactivity Series Order: Potassium > Sodium > Calcium > Magnesium > Aluminium > Zinc > Iron > Lead > Copper > Silver > Gold

Core Concept

Key point: The reactivity series arranges metals from most reactive (potassium) to least reactive (gold).

Detailed Explanation

1. Highly Reactive Metals

Characteristics:

- These metals react vigorously with cold water, steam, and acids, releasing hydrogen gas.

Examples: Potassium (K), Sodium (Na), Calcium (Ca)

With cold water: Form hydroxides and hydrogen gas.

2K_(s) + 2H₂O_(l) → 2KOH_(aq) + H_2(g)

With acids: Form salts and hydrogen gas.

2K_(s) + 2HCl_(aq) → 2KCl_(aq) + H_2(g)

Key point: Highly reactive metals react vigorously with cold water, steam, and acids.

2. Moderately Reactive Metals

Characteristics:

• These metals react:
• Slowly or not at all with cold water.
• With steam to form oxides and hydrogen gas.
• With acids to form salts and hydrogen gas.

Examples: Magnesium (Mg), Aluminium (Al), Zinc (Zn), Iron (Fe)

With cold water: Limited or no reaction (e.g., Mg reacts very slowly).

With steam: Form oxides and hydrogen gas.

Mg_(s) + H₂O_(g) → MgO_(s) + H_2(g)

With acids: React more slowly compared to highly reactive metals.

Mg_(s) + 2HCl_(aq) → MgCl_2(aq) + H_2(g)

Key point: Moderately reactive metals react with steam and acids but not significantly with cold water.

3. Less Reactive Metals

Characteristics:

• These metals:
• Do not react with cold water or steam.
• React slowly or not at all with acids.

Examples: Lead (Pb), Copper (Cu), Silver (Ag)

With cold water: No reaction.

With steam: No reaction.

With acids: Lead reacts slowly with strong acids, while copper and silver do not react.

Key point: Less reactive metals do not react with cold water or steam and react slowly or not at all with acids.

4. Unreactive Metals

Characteristics:

- These metals are the least reactive and do not react with cold water, steam, or acids under normal conditions.

Examples: Gold (Au), Platinum (Pt)

Key point: Unreactive metals do not react with cold water, steam, or acids under normal conditions.

Reactivity Series (Simplified Order)

The simplified order of the reactivity series is:

Potassium > Sodium > Calcium > Magnesium > Aluminium > Zinc > Iron > Lead > Copper > Silver > Gold

Key point: This arrangement reflects the decreasing reactivity of metals with acids, cold water, and steam.

Summary Table

Intermediate Level

Reactivity series order: K > Na > Ca > Mg > Al > Zn > Fe > Pb > Cu > Ag > Au

Groups:

• React vigorously with cold water, steam, and acids.
• Examples: K, Na, Ca.

• React slowly or not at all with cold water.
• React with steam to form oxides and hydrogen gas.
• React with acids to form salts and hydrogen gas.
• Examples: Mg, Al, Zn, Fe.

• Do not react with cold water or steam.
• React slowly or not at all with acids.
• Examples: Pb, Cu, Ag.

• Do not react with cold water, steam, or acids.
• Examples: Au, Pt.

Key point: The reactivity series helps us understand and predict the chemical behaviour of metals.

Important Points

• - Reactivity series = arrangement of metals in order of decreasing reactivity.
• - Simplified order:
• K > Na > Ca > Mg > Al > Zn > Fe > Pb > Cu > Ag > Au
• - Four groups:
• 1. Highly Reactive — K, Na, Ca
• 2. Moderately Reactive — Mg, Al, Zn, Fe
• 3. Less Reactive — Pb, Cu, Ag
• 4. Unreactive — Au, Pt
• - Highly Reactive Metals react vigorously with cold water, steam, and acids.
• - Moderately Reactive Metals react with steam and acids; slow or no reaction with cold water.
• - Less Reactive Metals do not react with cold water or steam; slow or no reaction with acids.
• - Unreactive Metals do not react with cold water, steam, or acids.
• - The reactivity series reflects the decreasing reactivity of metals with acids, cold water, and steam.

Remember

• - Reactivity series: K > Na > Ca > Mg > Al > Zn > Fe > Pb > Cu > Ag > Au.
• - Four groups:
• 1. Highly Reactive (K, Na, Ca)
• 2. Moderately Reactive (Mg, Al, Zn, Fe)
• 3. Less Reactive (Pb, Cu, Ag)
• 4. Unreactive (Au, Pt)
• - Highly reactive: vigorous with cold water, steam, acids.
• - Moderately reactive: react with steam and acids.
• - Less reactive: no reaction with cold water or steam.
• - Unreactive: no reaction with cold water, steam, or acids.
• - Reactivity depends on tendency to lose electrons.

Common Mistakes

Quick Revision

Reactivity Series:

Metals can be arranged into a reactivity series based on their observed reactions with acids, cold water, and steam. Metals can be grouped into four groups.

• 1. Highly Reactive Metals:
• These metals react vigorously with cold water, steam, and acids, releasing hydrogen gas.
• Examples: Potassium (K), Sodium (Na), Calcium (Ca)

• With cold water: Form hydroxides and hydrogen gas.
• 2K_(s) + 2H₂O_(l) → 2KOH_(aq) + H_2(g)

• With acids: Form salts and hydrogen gas.
• 2K_(s) + 2HCl_(aq) → 2KCl_(aq) + H_2(g)

• Slowly or not at all with cold water.
• React with steam to form oxides and hydrogen gas.
• React with acids to form salts and hydrogen gas.

With cold water: Limited or no reaction (e.g., Mg reacts very slowly).

• With steam: Form oxides and hydrogen gas.
• Mg_(s) + H₂O_(g) → MgO_(s) + H_2(g)

• With acids: React more slowly compared to highly reactive metals.
• Mg_(s) + 2HCl_(aq) → MgCl_2(aq) + H_2(g)

• Do not react with cold water or steam.
• React slowly or not at all with acids.

• With cold water: No reaction.
• With steam: No reaction.
• With acids: Lead reacts slowly with strong acids, while copper and silver do not react.

• 4. Unreactive Metals:
• These metals are least reactive and do not react with cold water, steam, or acids under normal conditions.
• Examples: Gold (Au), Platinum (Pt)

• Reactivity Series (Simplified Order):
• Potassium > Sodium > Calcium > Magnesium > Aluminium > Zinc > Iron > Lead > Copper > Silver > Gold

This arrangement reflects their decreasing reactivity with acids, cold water, and steam.

60-Second Revision

• Reactivity series: K > Na > Ca > Mg > Al > Zn > Fe > Pb > Cu > Ag > Au.
• Four groups:
• Highly reactive: vigorous with cold water, steam, acids.
• Moderately reactive: react with steam and acids.
• Less reactive: no reaction with cold water or steam.
• Unreactive: no reaction with cold water, steam, or acids.
• Reactivity depends on tendency to lose electrons.
• ⚠️ Warning: the reactivity series helps predict how a metal will behave in different reactions — always refer to it when predicting metal reactivity.