Reactivity Series of Metals

What is reactivity series?

A reactivity series is a series of metals based on their reactivity from highest to lowest. Thus, a metal reactivity series can be defined as a series of metals in order of reactivity from highest to lowest. It is also known as a series of activities. The reactivity of metals is due to their incomplete outer orbitals or their electron configuration. Metals form positively charged ions because they tend to lose electrons. Metals with high atomic numbers are more reactive because their electrons are far from the positively charged nucleus; thus, they can be easily removed.

Reactivity Series of Metal chart are given below:

Utility of Reactivity Series

The reactivity series is very useful as it gives the following information:

• The metal which is higher in the activity series is more reactive than the other. Lithium is the most reactive and platinum is the least reactive metal.

• The metals which have been placed above hydrogen are more reactive than hydrogen and can displace hydrogen from its compounds like water and acids to liberate hydrogen gas.

• The metals which are placed below hydrogen are less reactive than hydrogen and cannot displace hydrogen from its compounds like water and acids.

• A more reactive metal (placed higher in the reactivity series) can displace the less reactive metal from the solution of its salt.

• Metals at the top of the series are very reactive and, therefore, they do not occur free in nature, while the metals at the bottom of the series are least reactive and, therefore, they normally occur free in nature.

Salient Features

• Metals at the top of the series of reactivity are strong reducing agents because they oxidize quickly. These metals tarnish/corrode very easily.
• The reducing power of metals weakens as you go through the series.
• Electropositivity of elements also decreases as one moves down the metal reactivity series.
• All metals above hydrogen in the activity range release hydrogen gas when reacted with dilute HCl or dilute H2SO4.
• Metals placed high in the reactivity series can displace metals lower in their salt solutions.
• Higher category metals require more energy to isolate from ores and other compounds.

Reaction Between Metals and Water

Calcium and metals that are more reactive than calcium in the reactivity series can react with cold water to form the corresponding hydroxide, releasing hydrogen gas. For example, the reaction between potassium and water yields potassium hydroxide and hydrogen gas as described by the chemical equation below.

2K + 2H₂O → 2KOH + H₂

Reaction Between Metals and Acids

Lead and the metals are on high lead on the activity series form salts when reacted with sulphuric acid or hydrochloric acid. These reactions also contain the liberation of hydrogen gas. The reaction between sulphuric acid and zinc is an example of such a reaction. Here, zinc sulfate and H2 gas are formed as products. The chemical equation is:

Zn + H₂SO₄ → ZnSO₄ + H₂

Important Uses of Reactivity Series

• In displacement reaction - Displacement reactions are that reactions in which more reactive metal displaces less reactive metal from its salt. So, by reactivity series, you can also tell that which metal will displace another metal.

• The reaction between metals and water - Metals from potassium to calcium will react with cold water to release hydrogen gas.

Chemical Equations for the reaction of K and Ca with cold water are:

K (s) + H₂O (l) → KOH (aq) + ½ H2 (g) [Potassium Cold Water Potassium Hydroxide Hydrogen]

Note: Potassium reacts extremely violently with water to form a colorless aqueous solution of KOH with a release of12 mole of H₂ gas. The resultant solution is basic because of the dissolved hydroxide.

• The reaction between metals and acids - Lead and other different metals that are more reactive than lead in the reactivity series can react with hydrochloric acid and sulphuric acid to form salts. Thus, we are able to predict the reactions by reactivity series. Chemical Equations for the reaction of Pb with HCl and HSO₄ to form salts are:

Pb (s) + 2HCl (aq) → PbCl₂ (aq) + H₂ (g) [Lead Hydrochloric Acid Lead Chloride Hydrogen]

Note: Pb reacts slowly with acids like HCl and HNO₃ and releases bubbles of Hydrogen gas on reaction.

• Single displacement reaction between metals The high-ranking metals on the reactivity series usually reduce the ions of the low-ranking metals. Thus the high-ranking metal simply displaces the low-ranking metal in a single displacement reaction which occurs b/w them. One of the common displacement reactions is the displacement of copper from copper sulfate by zinc the chemical equation for this reaction is given by:

Zn (s) + CuSO₄ (aq) → ZnSO₄ (aq) + Cu (s)

This concept is also used in various applications, mostly for the extraction of metals. For example, with the help of the single displacement reaction with magnesium titanium can be extracted from titanium tetrachloride. Thus to predict the result of the single displacement reaction, the reactivity series becomes very helpful.

Frequently Asked Question (FAQs)

Q1. What does reactivity series depend on?

Ans. The reactivity series of metals totally depends on the reactivity of metals which is dependent on the atomic radius, nuclear charge, sublevel electrons arrangement, and shielding effect.

Q2. What is meant by reactivity series of metals?

Ans. A reactivity series of metals is a table listing metals to decrease reactivity. Usually, the more reactive a metal is:, the more vigorously it reacts with different substances. It quickly loses electrons to form positive ions (cations).

Q3. How is reactivity series formed?

Ans. In a reactivity series, the most reactive element is placed at the top and the least reactive element at the bottom. The more reactive metals tend to lose electrons and form positive ions.

Q4. Which metal is most reactive?

Ans. According to the reactivity series, sodium is the most reactive metal.

Q5. Which is the least reactive metal?

Ans. The least reactive metal is Platinum. It has corrosion resistance, even at high temperatures, and is considered a noble metal. Therefore, Platinum is often found chemically uncombined as native Platinum.