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Question: Electron affinities of O,F,S and Cl are in the order....

Electron affinities of O,F,S and Cl are in the order.

A

O < S < Cl < F

B

O < S < F < Cl

C

S < O < Cl < F

D

S < O < F < Cl

Answer

O < S < F < Cl

Explanation

Solution

  1. General Trend: Electron affinity generally increases across a period and decreases down a group.

  2. Exceptions: Due to their small size and high electron density, elements of the second period (like O and F) experience significant interelectronic repulsion when an electron is added. This makes their electron affinity less favorable (less negative) compared to their respective third-period counterparts (S and Cl).

    • Therefore, EA(S) > EA(O) and EA(Cl) > EA(F).

  3. Halogens vs. Chalcogens: Halogens (F, Cl) generally have higher electron affinities than chalcogens (O, S) because gaining an electron allows them to achieve a stable noble gas configuration.

  4. Combining the trends:

    • We know O < S.
    • We know F < Cl.
    • Comparing across groups, halogens are generally higher than chalcogens.
    • The actual values are approximately: EA(O) ≈ -141 kJ/mol, EA(S) ≈ -200 kJ/mol, EA(F) ≈ -328 kJ/mol, EA(Cl) ≈ -349 kJ/mol. (Note: A more negative value indicates higher electron affinity, meaning more energy is released).
    • Arranging in increasing order (from least negative to most negative): O < S < F < Cl.