Problem 61 - A Complete Resource Book in Chemistry for JEE Main

Question

The electron affinities of \(\mathrm{N}, \mathrm{O}, \mathrm{S}\) and \(\mathrm{Cl}\) are (a) \(\mathrm{O} \approx \mathrm{Cl}<\mathrm{N} \approx \mathrm{S}\) (b) \(\mathrm{O}<\mathrm{S}<\mathrm{Cl}<\mathrm{N}\) (c) \(\mathrm{N}<\mathrm{O}<\mathrm{S}<\mathrm{Cl}\) (d) \(O<\mathrm{N}<\mathrm{Cl}<\mathrm{S}\)

Step-by-Step Solution

Answer

C. CN< ext{O}< ext{S}< ext{Cl} D.

Step 1: Understanding Electron Affinity

Electron affinity is the amount of energy released when an electron is added to a neutral atom in the gaseous state. Generally, nonmetals have higher electron affinity because they usually gain electrons to achieve a noble gas configuration.

Step 2: Recognizing the Trend in the Periodic Table

In the periodic table, electron affinity generally increases across a period from left to right and decreases down a group. Exceptions exist due to electron-electron repulsion or atomic configuration.

Step 3: Analyzing Each Element Individually

- **Nitrogen ( C ext{N} D):** This element has a half-filled p subshell, making it less eager to gain an additional electron. - **Oxygen ( C ext{O} D):** Oxygen is more eager to gain an electron due to its position in the periodic table but is somewhat stable with its electron configuration. - **Sulfur ( C ext{S} D):** Sulfur is less electronegative than oxygen but more than nitrogen comparatively. - **Chlorine ( C ext{Cl} D):** Known for its strong tendency to gain extra electron, making chlorine have one of the highest electron affinities.

Step 4: Comparing Electron Affinities of Elements

Given the above information, compare the electron affinities: - CCl D E> S > O > N D, since chlorine wants to complete its shell. - Sulfur, being below oxygen in the periodic table, has higher electron affinity than oxygen but less than chlorine. - Since nitrogen is close to a stable configuration, its electron affinity is less than the others.

Key Concepts

Periodic Table Trends

In the periodic table, elements are arranged in an order that reveals several key trends, including electron affinity. As you move from left to right across a period, generally, electron affinity increases. This is because atoms become more eager to gain electrons to reach a stable octet configuration.
However, there are exceptions due to electron repulsion or unique electron configurations like those of half-filled or fully filled subshells.
On the other hand, as you move down a group, electron affinities often decrease. This is because larger atoms have electrons that are farther from the nucleus. The increased distance weakens the attraction between the nucleus and an additional electron. Thus, atoms in lower periods tend to have lower electron affinities than those higher up in the same group.

Nitrogen Electronic Configuration

Nitrogen, with an electronic configuration of \[ 1s^2 2s^2 2p^3 \], has a half-filled p subshell which is relatively stable. Because of this configuration, nitrogen does not have a strong tendency to gain another electron.
Adding an electron would disrupt this balance and increase electron-electron repulsion in the already half-filled subshell.
As a result, nitrogen's electron affinity is relatively low compared to other nonmetals like oxygen, sulfur, or chlorine, which demonstrate a stronger tendency to attract additional electrons in order to achieve a more stable configuration.

Nonmetal Characteristics

Nonmetals exhibit various characteristics including higher electron affinities compared to metals. This is mainly because nonmetals tend to gain electrons to achieve full outer shells or to complete their octet in the p subshell.
- They are generally more electronegative and desire electrons strongly. - Nonmetals become more reactive as they possess higher electron affinities.
For example, elements such as oxygen and chlorine are highly reactive nonmetals. Their electron affinities contribute to their ability to form bonds by gaining electrons from less electronegative elements. This is an essential aspect of chemical bonding in organic and inorganic reactions.

Halogens Electron Affinity

Halogens, a group in the periodic table which includes chlorine, have some of the highest electron affinities of all elements. This is because halogens need just one more electron to achieve a noble gas configuration, making them very potent in attracting extra electrons.
- Chlorine, in particular, has a very strong electron affinity. It releases a considerable amount of energy when it gains an electron, more than elements like sulfur or oxygen.
This high electron affinity explains why halogens are highly reactive, especially with alkali metals, to form stable ionic compounds. The desire to achieve a stable electron count similar to noble gases like argon drives this characteristic, making halogens some of the most reactive nonmetals on the periodic table.