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NEET CHEMISTRYClassification of Elements and Periodicity in PropertiesMedium

Question

The correct order of increasing electron gain enthalpy with a negative sign for the elements O, S, F, and Cl is:

A

Cl < F < S < O

B

O < S < F < Cl

C

F < S < O < Cl

D

S < O < Cl < F

Step-by-Step Solution

Electron gain enthalpy becomes more negative across a period (left to right) and less negative down a group. However, there are significant anomalies due to atomic size.

  1. Group Comparison: Group 17 elements (F, Cl) have higher effective nuclear charge and are closer to a stable octet than Group 16 elements (O, S). Thus, Halogens have more negative electron gain enthalpies than Chalcogens.
  2. Size Anomaly:
  • F vs Cl: Fluorine is very small (n=2 shell). The incoming electron faces strong inter-electronic repulsion. Chlorine (n=3 shell) is larger and accommodates the electron more easily. Thus, Cl has a more negative value than F.
  • O vs S: Similarly, Oxygen is very small, leading to repulsion. Sulfur has a more negative value than Oxygen.
  1. Overall Order of Negative Magnitude: Chlorine (Most negative: -349 kJ/mol) Fluorine (-328 kJ/mol) Sulfur (-200 kJ/mol) Oxygen (Least negative: -141 kJ/mol)
  2. Increasing Order: O < S < F < Cl.

Exam Context & Concepts Covered

This question aligns with the NEET CHEMISTRY syllabus, specifically targeting concepts from Classification of Elements and Periodicity in Properties. Mastering this topic is crucial for scoring well in the upcoming medical entrance examinations. Solving conceptually related problems will help you understand the nuances of these concepts and improve your problem-solving speed.

CHEMISTRYClassification of Elements and Periodicity in Propertiescorrectincreasingelectronenthalpynegative

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B.Ca²⁺ < Ar < K⁺
C.Ca²⁺ < K⁺ < Ar
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Which one of the following represents all isoelectronic species?

A.Na⁺, Cl⁻, O⁻, NO⁺
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A.+10.2 eV
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C.–10.2 eV
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A.H⁺
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C.Na⁺
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A.$Ca^{2+} < K^+ < Ar < S^{2-} < Cl^-$
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A.Si < C < O < N < F
B.O < F < N < C < Si
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A.Cr > Mn > V > Ti
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