Problem 138 - A Complete Resource Book in Chemistry for JEE Main

Question

Select the incorrect statement: (a) Fluorine cannot show oxidation number greater than zero (b) Halogens do not directly combine with oxygen (c) Iodine can not displace chlorine from \(\mathrm{KClO}_{3}\) (d) Euchlorine is a mixture of \(\mathrm{Cl}_{2}\) and \(\mathrm{Cl}_{2} \mathrm{O}_{7}\)

Step-by-Step Solution

Answer

Statement (d) is incorrect; euchlorine is a mixture of Cl2 and Cl2O, not Cl2O7.

Step 1: Analyze Statement (a)

Fluorine is the most electronegative element and has only one oxidation state of 0 when in its molecular form (F_2 ight) or in negative oxidation states in compounds. It doesn’t have any oxidation numbers greater than zero as it can never lose its lone valence electron to show a positive oxidation state.

Step 2: Analyze Statement (b)

Halogens like fluorine, chlorine, bromine, and iodine can react with oxygen to form various oxyacids and oxygen-containing compounds. Nevertheless, halogens (except fluorine under specific conditions) do not directly combine with oxygen. Instead, they form compounds with oxygen often involving intermediary steps.

Step 3: Analyze Statement (c)

Iodine is less reactive compared to chlorine and cannot displace chlorine in a compound. Since chlorine is more electronegative and reactive, iodine cannot displace chlorine from KClO_3 .

Step 4: Analyze Statement (d)

Euchlorine is a historical term referring to a mixture of Cl_2 and Cl_2O , not Cl_2O_7 . Cl_2O_7 is different from the more commonly addressed Cl_2O in euchlorine mixtures, making this statement incorrect.

Key Concepts

Oxidation States

The concept of oxidation states is crucial in understanding how atoms interact in chemical compounds. An oxidation state is a theoretical charge on an atom if we assume that an atom's share of each electron pair is completely transferred to the more electronegative atom. In simple terms, it's a number that represents the count of electrons an atom gains, loses, or appears to use in bonding. Each element has a normal oxidation state that it prefers. Fluorine often serves as a valuable example because, unlike other elements, it has a consistent oxidation state everywhere except in its natural form. As the most electronegative element, it usually has an oxidation state of  since it aggressively attracts electrons. This powerful electronegativity means fluorine is never found with a positive oxidation state in any of its compounds.

Fluorine

Fluorine is a fascinating element due to its exceptional reactivity and powerful electronegativity, the highest among all elements. This makes it a unique player in chemical reactions:

• Fluorine readily bonds with almost all elements, except noble gases under standard conditions, forming fluoride ions () in compounds.
• Its ability to pull electrons strongly to itself results in stable compounds where it maintains a  oxidation state.
• When fluorine forms compounds, it takes three electrons, resulting in some of the most electronegative and stable nonmetallic compounds known.

Understanding fluorine's reactivity is essential for appreciating its role in complex chemical mechanisms and knowing why it doesn't show positive oxidation states.

Oxygen Compounds

While many elements can form compounds directly with oxygen, halogens behave differently. They often require specific conditions or indirect methods to form compounds with oxygen.

• Typically, oxygen compounds of halogens, known as "oxoacids," involve intermediary steps or reactions.
• Common oxygen compounds include hypochlorous acid (_2O) and perchloric acid (_4O_{6}).
• Fluorine can directly bond with oxygen but usually doesn't form oxoacids like other halogens due to its strong electronegativity.

Halogen-oxygen compounds display various oxidation states and reactivity, making them significant in industrial and chemical processes.

Iodine Displacement

Iodine displacement in chemical reactions can be intriguing since it highlights the varying reactivity levels among halogens. In the halogen group, reactivity decreases as you move from fluorine to iodine. This decrement has practical implications:

• Iodine is less reactive than chlorine or bromine, limiting its capability to displace these elements in compounds.
• For example, in a compound like _3, iodine cannot replace chlorine because the reactivity cascade is influenced by electronegativity and energy considerations.
• This reactivity trend explains why iodine is incapable of participating in certain displacements, emphasizing its potential roles in different chemical contexts.

By understanding this reactivity order, we gain insights into how halogen reactions are managed and predicted in both natural and synthetic chemistry contexts.