Question

Explain why $ICl$ is more reactive than ${{I}_{2}}$.

Answer 1

Hint : The key to solving this question is to think about what kind of bonds, the bonds between $I-Cl$ and $I-I$ are. Also consider the effect different electronegativities may have on these bonds.

Complete step by step solution:
Both $I-Cl$ and $I-I$ consist of covalent bonds that bond both the atoms together. Covalent bonds are found as both the atoms are halogens and can share electrons to get a stable electronic configuration. Since, $I-I$ has 2 iodine atoms, the nature of this bond is completely covalent. Due to the difference of electronegativities between $I$ and $Cl$, the bond $I-Cl$ has a slightly ionic nature. This ionic nature causes the bond to be weaker than its counterpart, the covalent bond. A weaker bond can be broken more easily and is considered to be more reactive than a completely covalent bond.
In general, all inter-halogen bonds are found to be weaker and more reactive than other exclusively covalent bonds found between two halogens of the same species. There is quite a noticeable change in electronegativities as we go down the halogen group when compared to the change in electronegativities of any other group. This makes the ionic or polar nature of the inter-halogen bonds more apparent.

Hence, $ICl$ is more reactive than ${{I}_{2}}$ due to the ionic nature of the $I-Cl$ bond.

Note : We know that often $Cl$ forms stronger bonds than $I$ in a variety of compounds and are usually less reactive like $HCl$ and $C{{H}_{3}}Cl$ against $HI$ and $C{{H}_{3}}I$. Please do not get confused due to this, here the size and electronegativity of $Cl$ makes the bond stronger. Whereas when the bond is formed between the atoms of the same group, the same attributes make the bond weaker and the molecule more reactive.