Problem 37 - 43 Years JEE ADVANCED (1978-2020) + JEE MAIN Chapterwise & Topicwise Solved Papers Chemistry

Question

Statement-1: \(\mathrm{F}\) atom has less electron affinity than \(\mathrm{Cl}\) atom. Statement-2 : Additional electrons are repelled more effectively by \(3 p\) electrons in \(\mathrm{Cl}\) atom than by \(2 p\) electrons in \(\mathrm{F}\) atom [1998 - 2 Marks] (a) Statement-1 is True, Statement-2 isTrue; Statement-2 is a correct explanation for Statement-1 (b) Statement-1 is True, Statement-2 is True; Statement-2 is NOT a correct explanation for Statement-1 (c) Statement- 1 is True, Statement-2 is False (d) Statement- 1 is False, Statement- 2 is True.

Step-by-Step Solution

Answer

(b) Statement-1 is True, Statement-2 is True; Statement-2 is NOT a correct explanation for Statement-1.

Step 1: Understand Electron Affinity

Electron affinity is the energy change that occurs when an electron is added to an isolated atom in the gaseous state. Generally, as we move across a period from left to right in the periodic table, the electron affinity increases as the nuclear charge increases.

Step 2: Compare Electron Affinity of F and Cl

Fluorine and chlorine are both halogens, where theoretically, fluorine should have a higher electron affinity because it is more electronegative. However, chlorine has a higher electron affinity than fluorine. This anomaly is often credited to electron-electron repulsion in the small, compact 2p orbitals of fluorine.

Step 3: Analyze Statement-1

Statement-1 claims that fluorine has less electron affinity than chlorine, which holds true due to the increased electron-electron repulsion in the smaller fluorine atom, making chlorine more favorable for additional electrons.

Step 4: Evaluate Statement-2

Statement-2 suggests that 3p electrons in chlorine repel incoming electrons less effectively than 2p electrons in fluorine due to greater spatial distribution, which is true as it reduces repulsion and makes it easier for chlorine to gain an extra electron.

Step 5: Determine if Statement-2 Explains Statement-1

While both statements are individually correct, Statement-2 is focused on explaining electron repulsion in p orbitals rather than directly explaining why chlorine has a higher electron affinity than fluorine. Therefore, Statement-2 is not a direct explanation for Statement-1.

Key Concepts

Periodic Table Trends

Understanding periodic table trends is essential for mastering concepts in chemistry. One such trend is electron affinity, which refers to the tendency of an atom to accept an extra electron. Across a period in the periodic table from left to right, electron affinity generally increases. This trend is due to the increasing nuclear charge, which pulls additional electrons closer to the nucleus.

However, there are exceptions to this trend, as seen with fluorine (\( \mathrm{F} \)) and chlorine (\( \mathrm{Cl} \)). Chlorine, which is located below fluorine in the same group, has an unexpectedly higher electron affinity. This anomaly occurs due to different factors such as electron-electron repulsion, which we will explain later. Observing these trends helps predict how different elements will interact chemically and can clarify exceptions found in empirical data.

Electron-Electron Repulsion

Electron-electron repulsion is an important concept in understanding why certain elements exhibit unexpected properties in electron affinity. Inside an atom, electrons are negatively charged particles. When electrons are added to a system, their negative charges naturally repel each other.

This repulsion is particularly significant in smaller atoms like fluorine, where the electrons are crowded into the smaller 2p orbitals. In these tight spaces, electrons repel each other more intensely than in larger orbitals. As a result, adding an electron to fluorine is less favorable compared to chlorine, which has larger 3p orbitals providing more space. Thus, chlorine experiences less electron-electron repulsion, allowing it to more easily accommodate an extra electron.

In summary, electron-electron repulsion helps explain anomalies in periodic trends, like why chlorine has a higher electron affinity than fluorine, despite being below it in the periodic table.

p Orbitals

The concept of p orbitals is pivotal when discussing electron affinity and electron repulsion. Unlike s orbitals that are spherical, p orbitals have a dumbbell shape and come in three orientations: px, py, and pz. These orbitals are part of the outer electron shell and are crucial in forming chemical bonds.

In fluorine, the electrons add into the 2p orbitals, which are relatively compact. This compactness leads to increased electron-electron repulsion when an extra electron is added, making it difficult for the electron to be accommodated. On the other hand, the 3p orbitals in chlorine are larger and more spread out. This spatial difference allows chlorine to accept an extra electron with less repulsion than in fluorine, contributing to its higher electron affinity.

Understanding how p orbitals work is key to comprehending how different elements interact with additional electrons. It highlights why structures like 3p orbitals in chlorine are more accommodating compared to the 2p orbitals in fluorine.