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Activity Series of Non Metals

There are many elements which show difference in the chemical reactivity with each other. We can determine the relative reactivity with the help of activity series of elements which is also known as reactivity series. In this series, elements are arranged in increasing order of their reactivity compare to others. In other words; the reactivity decreases from top to bottom in the series.

The top most elements are more reactive while bottom elements are least reactive in nature. In a displacement reaction, more reactive element can replace the less reactive element therefore this series of element is quite helpful in the prediction of products. Elements which are placed at more distance in the series can react more vigorously compare to those elements which are placed close to each other in the activity series. We know that a metal with low electro-negativity and low ionisation potential is more reactive, hence is placed at the top of series. For example; the activity series of metal starts from alkali metals because they have least ionisation potential and most reactive compare to other metals. These metals can easily replace H from water in the form of H2 gas and act as good reducing agents.

Therefore they will be weak oxidising agents and their ions cannot reduce to metal in their aqueous solution. Similarly most reactive metals react rapidly with air to form oxides. Aluminium is exceptional case as it has a coating of Al2O3 which prevents the further oxidation. On the contrary, Fe reacts with O2 to form rust and the phenomenon is known as corrosion. The Nobel metals such as Pt, Au are placed at the bottom of the series as they are least reactive and do not corrode easily. Just like metals, non-metals can also arrange on reactivity series. Non-metals are electronegative elements which tend to accept electrons and form anions during redox reactions.  They act as strong oxidizing agents. The most reactive non-metal is placed at the top while least reactive appear on the bottom. Hence non-metals are arranged in ordered of their oxidising strength. Let’s discuss one the reactivity series of non-metals of 17th group.

The reactivity of halogens decreases from fluorine to iodine. Hence fluorine is most reactive and iodine is least reactive element. That is the reason; fluorine cannot isolate it in the laboratory very easily. In terms of oxidising power, Cl2 is the best oxidising agent, hence it can displace Br2 from solutions containing Br- ion;

Cl2 + 2Br-   Br2 + 2Cl-

Here Cl2 acts as oxidising agent and remove electrons from Br- to form Br2 which turns the solution orange or red colour. Similarly Br2 can iodine from solutions containing I- ions as given below;

Br2 + 2I-  I2 + 2Br-

The liberation of I2 can be detected with the change in colour from brown to violet colour due to I2. The addition of starch indicator to same solution turns it to blue-black solution due to the formation of starch-iodine complex. We can predict the products of the reaction of Cl2 with I- ions.

Since Cl2 can displace I0 ions from its solution which can be visualised due to change in colour. But the reverse reaction is not possible i.e. I2 cannot displace Cl- ions from its solution as I2 is a weak oxidising agent.