Problem 65 - A Complete Resource Book in Chemistry for JEE Main

Question

Which of the following is the correct relation with regard to the electron afinity of halogen? (a) \(\mathrm{F}>\mathrm{Cl}\) (b) \(\mathrm{F}>\mathrm{I}\) (c) \(\mathrm{Br}>\mathrm{F}\) (d) \(\mathrm{Br}>\mathrm{Cl}\)

Step-by-Step Solution

Answer

The correct relation is (b) 52>52.

Step 1: Understanding the Concept

Electron affinity refers to the amount of energy released when an electron is added to a neutral atom to form an anion. Halogens generally have high electron affinities as they are one electron away from a full outer shell.

Step 2: Halogen Electron Affinities

Typically, chlorine (52) has the highest electron affinity among the halogens, followed by fluorine (52), bromine (52), and iodine (52). Fluorine doesn't have the highest affinity due to its small atomic size, which results in increased electrostatic repulsion among electrons.

Step 3: Analyze Each Option

Review the provided options: (a) 52>52 suggests fluorine has a higher electron affinity than chlorine, but actually, chlorine has a higher affinity. (b) 52>52 is correct because fluorine has a higher electron affinity than iodine. (c) 52>52 suggests bromine has a higher electron affinity than fluorine, which is incorrect. (d) 52>52 suggests bromine has higher electron affinity than chlorine, which is also incorrect.

Step 4: Determine the Correct Answer

From the analysis, only option (b) 52>52 correctly describes the relationship between the electron affinities of these halogens. Fluorine does have a higher electron affinity compared to iodine.

Key Concepts

Halogens

Halogens are a group of elements found in Group 17 on the periodic table. They include fluorine (F), chlorine (Cl), bromine (Br), iodine (I), and astatine (At). These elements are highly reactive and are characterized by having seven electrons in their outermost shell. This makes them eager to gain an additional electron to achieve a full set of eight valence electrons, similar to the stable noble gases. Halogens are highly electronegative, meaning they have a strong tendency to attract electrons from other atoms during chemical reactions. This property makes them particularly effective in forming compounds, especially salts. The reactivity of halogens decreases as you move down the group from fluorine to iodine due to an increase in atomic size and a decrease in electronegativity.

Key properties of halogens include:

• High electronegativity
• Strong oxidizing abilities
• Reactive with metals to form salts
• Exist as diatomic molecules (e.g., F₂, Cl₂) in their elemental form

Understanding halogens is essential to grasping concepts like electron affinity and the formation of anions.

Anion Formation

Anions are negatively charged ions formed when an atom gains one or more electrons. In the case of halogens, the gaining of an additional electron fills their outermost electron shell, leading to a stable electron configuration. This process is what makes halogens so eager to participate in anion formation; it's almost like achieving electron nirvana for these elements.

When an electron is added to a neutral halogen atom, the energy associated with this addition is captured and the newly formed ion is more stable than the original atom. In essence, halogens form anions through the spontaneous acquisition of electrons. This leads to halide ions such as fluoride (F^-), chloride (Cl^-), bromide (Br^-), and iodide (I^-).

The steps of anion formation are:

• An electron is added to a halogen atom.
• The atom releases energy upon gaining the electron.
• The result is a negatively charged ion or anion.

Halogens exhibit a high drive towards forming anions due to their desire to achieve a complete octet in their valence shell.

Electron Energy Release

Electron affinity is a key concept related to electron energy release. It describes the energy change that occurs when an electron is added to a neutral atom in the gaseous state, forming an anion. This process usually releases energy, which is why electron affinities for elements like halogens are typically negative values.

The electron energy release during this process signifies how much an atom wants to gain an additional electron. For halogens, the eagerness to achieve a full valence shell means they release a substantial amount of energy when forming an anion. Chlorine, for example, has a particularly high electron affinity, greater than that of even fluorine, due to a combination of factors such as atomic size and electron repulsion forces.

Some aspects affecting electron energy release include:

• The size of the atom: Smaller atoms often have higher electron affinities.
• The nuclear charge: A higher positive charge can result in stronger attractions.
• Electron-electron repulsions within the atom.

Understanding electron energy release helps clarify why certain halogens are more reactive and eager to form anions than others.