Problem 116 - A Complete Resource Book in Chemistry for JEE Main

Question

Regarding \(\mathrm{F}^{-}\)and \(\mathrm{Cl}^{-}\)which of the following statements is correct? 1\. Cl can give up an electron more easily than \(\mathrm{F}^{-}\) 2\. \(\mathrm{Cl}^{-}\)is a better reducing agent than \(\mathrm{F}^{-}\) 3\. \(\mathrm{Cl}^{-}\)is smaller in size than \(\mathrm{F}^{-}\) 4\. \(\mathrm{F}^{-}\)can be oxidized more readily than \(\mathrm{Cl}^{-}\) (a) 1,2 and 4 (b) 1 only (c) 1 and 2 (d) 3 and 4

Step-by-Step Solution

Answer

Correct options are 1 and 2 (Choice C).

Step 1: Analyze Oxidation Trends

Analyzing the tendency for oxidation, we know that the ability of a species to lose electrons is linked to being oxidized. Both \( \text{F}^- \) and \( \text{Cl}^- \) are anions, negatively charged atoms, meaning they have extra electrons compared to their neutral atoms. \( \text{F}^- \) is smaller and holds its electrons more tightly due to higher electronegativity, making \( \text{Cl}^- \) the better candidate to give up an electron and thus to be oxidized more easily.

Step 2: Evaluate Reducing Agent Ability

A reducing agent is a species capable of donating electrons to another species. \( \text{Cl}^- \), with its weaker hold on its outer electron compared to \( \text{F}^- \), can more readily donate an electron, making \( \text{Cl}^- \) a better reducing agent than \( \text{F}^- \).

Step 3: Consider Atomic Size

When considering the size of ions, \( \text{F}^- \) is generally smaller in size than \( \text{Cl}^- \). This trend fits with periodic trends where the size increases down the group (with \( \text{Cl}^- \) being below \( \text{F}^- \) in the same group on the periodic table).

Step 4: Final Assessment of Statements

Based on steps 1-3, recall the correct comparisons: \( \text{Cl}^- \) can give up an electron more easily and is a better reducing agent than \( \text{F}^- \), and \( \text{F}^- \) is indeed smaller than \( \text{Cl}^- \). Hence, statements 1 and 2 are correct, while statement 4, which suggests \( \text{F}^- \) can be oxidized more readily than \( \text{Cl}^- \), is incorrect.

Key Concepts

Oxidation Trends

Oxidation refers to the process where an atom or ion loses electrons. In the world of chemistry, this is an essential concept, especially when evaluating anions like \( \text{F}^- \) and \( \text{Cl}^- \). These ions have gained an electron compared to their neutral forms, making them negatively charged.

To determine which ion is more likely to undergo oxidation, we need to look at their electronegativity and size. Fluoride ions (\( \text{F}^- \)) are smaller and have a higher electronegativity compared to chloride ions (\( \text{Cl}^- \)). This means \( \text{F}^- \) holds its additional electron more tightly and is less likely to give it up. Hence, \( \text{Cl}^- \) is more prone to oxidation as it can lose its electron more easily than \( \text{F}^- \).

• \( \text{Oxidation:} \) Loss of electrons.
• \( \text{High electronegativity:} \) Provides stronger electron hold
• \( \text{\( \text{Cl}^- \) is more oxidizable than \( \text{F}^- \):} \) \( \text{Cl}^- \) is larger, holds its electron less tightly.

Reducing Agents

A reducing agent is a substance that donates electrons, causing another substance to be reduced. This donating capability makes them crucial players in redox reactions.

In comparing \( \text{F}^- \) and \( \text{Cl}^- \), the ability to act as reducing agents is determined by how readily they can give away electrons. Due to its larger size and weaker electron holding capacity, \( \text{Cl}^- \) acts as a better reducing agent than \( \text{F}^- \). The extra space in \( \text{Cl}^- \)'s electron cloud allows easier electron donation.

• \( \text{Reducing Agent:} \) Donates electrons.
• \( \text{\( \text{Cl}^- \) as a reducing agent:} \) Larger, with a weaker electron hold.
• \( \text{Electron donation capability:} \) Higher in \( \text{Cl}^- \) than \( \text{F}^- \).

Atomic Size

Atomic size, or ionic radius, is another crucial factor when discussing chemical behavior of anions like \( \text{F}^- \) and \( \text{Cl}^- \). This characteristic influences many properties, including oxidation and reducing potential.

Within the periodic table, atomic size increases as you move down a group. This puts \( \text{Cl}^- \) at a larger size compared to \( \text{F}^- \) since chlorine is located below fluorine. The extra electron shells in \( \text{Cl}^- \) result in a larger overall ion size.

• \( \text{Atomic size increases down a group:} \) More electron shells added.
• \( \text{\( \text{Cl}^- \) is larger than \( \text{F}^-\):} \) Due to additional electron shell.
• \( \text{Size influences reactivity:} \) Larger ions often have more significant reaction tendencies in redox processes.

Periodic Trends

Understanding periodic trends is indispensable for grasping chemistry's big picture. These trends help explain why elements behave differently, including their oxidation and size characteristics.

Elements in the same group of the periodic table show consistent trends in properties. For instance, as you progress down a group:

• \( \text{Atomic size increases:} \) Each element has an additional electron shell.
• \( \text{Electronegativity decreases:} \) Larger atoms have less electromagnetic pull on their electrons.
• \( \text{Ionization energy decreases:} \) Easier to remove electrons from larger atoms.

For \( \text{F}^- \) and \( \text{Cl}^- \):

• \( \text{\( \text{F}^- \) is smaller and more electronegative than \( \text{Cl}^- \)} \)
• \( \text{\( \text{Cl}^- \) is larger, has lower ionization energy, thus is better at electron donation.} \)

These periodic trends shed light on their oxidation capabilities, where \( \text{Cl}^- \) is more likely to lose an electron compared to the tightly held extra electron in \( \text{F}^- \). Knowing these patterns helps us predict and understand chemical behaviors across the periodic table.