Question

Increasing order of Electron affinity for following configuration. (A) 1s², 2s² 2p² (B) 1s², 2s² 2p⁴ (C) 1s², 2s² 2p⁶ 3s² 3p⁴ (D) 1s², 2s² 2p⁶, 3s² 3p³

• A. d < a < b < c
• B. d < a < c < b
• C. a < b < c < d
• D. a < b

Answer 1

Answer: (A)

d < a < b < c

Answer 2

To determine the increasing order of electron affinity, we first identify the elements corresponding to each electronic configuration:

• (A) $1s^2, 2s^2 2p^2$: This is the electronic configuration of Carbon (C). Carbon is in Period 2, Group 14.
• (B) $1s^2, 2s^2 2p^4$: This is the electronic configuration of Oxygen (O). Oxygen is in Period 2, Group 16.
• (C) $1s^2, 2s^2 2p^6 3s^2 3p^4$: This is the electronic configuration of Sulfur (S). Sulfur is in Period 3, Group 16.
• (D) $1s^2, 2s^2 2p^6, 3s^2 3p^3$: This is the electronic configuration of Phosphorus (P). Phosphorus is in Period 3, Group 15.

Now, let's compare their electron affinities based on periodic trends and exceptions:

1. General Trends: Electron affinity generally increases across a period (from left to right) due to increasing effective nuclear charge and decreasing atomic size, and generally decreases down a group due to increasing atomic size and shielding effects.

2. Exceptions/Special Cases:

• Half-filled/Fully-filled Subshells: Elements with stable half-filled ($p^3, d^5, f^7$) or fully-filled ($p^6, d^{10}, f^{14}$) subshells tend to have very low or even positive (energy absorbed) electron affinities because adding an electron would disrupt their stable configuration. Phosphorus (P) has a half-filled $3p^3$ configuration, making it relatively stable and thus having a very low electron affinity.
• Second Period vs. Third Period Elements: For elements in the same group, the electron affinity of a second-period element is generally less than that of the corresponding third-period element. This is because the second-period elements are very small, and the added electron experiences significant inter-electronic repulsion from the already existing electrons in the small 2p orbital, making the addition less favorable. Therefore, Electron Affinity of Sulfur (S) is greater than that of Oxygen (O).

Let's apply these principles to order the given elements:

• Phosphorus (D): With its half-filled $3p^3$ configuration, Phosphorus will have the lowest electron affinity among the given elements.

• Comparing Carbon (A) and Oxygen (B): Both are in Period 2. Oxygen (Group 16) is to the right of Carbon (Group 14). So, Electron Affinity of Oxygen is greater than that of Carbon. EA(O) > EA(C).

• Comparing Oxygen (B) and Sulfur (C): Both are in Group 16. Sulfur is in Period 3, and Oxygen is in Period 2. Due to the size effect and inter-electronic repulsion in the smaller 2p orbitals of Oxygen, Sulfur has a higher electron affinity than Oxygen. EA(S) > EA(O).

• Comparing Phosphorus (D) and Sulfur (C): Both are in Period 3. Sulfur (Group 16) is to the right of Phosphorus (Group 15). So, Electron Affinity of Sulfur is greater than that of Phosphorus. EA(S) > EA(P).

Combining these observations:

1. P (D) has the lowest electron affinity.
2. Among C (A), O (B), and S (C), we have EA(S) > EA(O) > EA(C).

Therefore, the increasing order of electron affinity is: Phosphorus (D) < Carbon (A) < Oxygen (B) < Sulfur (C)

In terms of the given labels: D < A < B < C.

Let's check with approximate experimental values (in kJ/mol):

• EA(P) $\approx$ 72
• EA(C) $\approx$ 122
• EA(O) $\approx$ 141
• EA(S) $\approx$ 200

The order D < A < B < C is consistent with these values.