The Question is from neet-chemistry classification-of-elements-and-periodicity-in-prop , and it was created by the author Mr. S M HUSSAIN

Question

Which of the following properties generally decreases across a period from left to right, but shows an anomalous increase at Group 15 elements compared to Group 14 and 16 elements?

Mr. S M HUSSAIN · Accepted Answer

## CORE INFORMATION
✓ **Answer**: D
## CONCEPT FRAMEWORK
 **Primary Concept**: Periodic Trends in Electron Gain Enthalpy
 **Related Topics**: Atomic structure, electron configuration, effective nuclear charge, shielding effect
 **Prerequisites**: Understanding of electron shells, subshells, and their filling order.
## SOLUTION PATHWAY
**Given Information**:
The question asks about a property that generally decreases across a period but shows an anomalous increase at Group 15 elements.
**Method & Steps**:
1. Analyze the periodic trends of each option:
  Reasoning: We need to examine how ionization enthalpy, atomic radius, electronegativity, and electron gain enthalpy change across a period and around Group 15.
  Formula/Rule: No specific formula, but understanding of periodic trends is crucial.
2. Identify the anomalous behavior at Group 15:
  Working: Let's analyze each option:
		* **Ionization enthalpy:** Generally increases across a period due to increasing effective nuclear charge.  No anomalous increase at Group 15.
		* **Atomic radius:** Generally decreases across a period due to increasing effective nuclear charge. No anomalous increase at Group 15.
		* **Electronegativity:** Generally increases across a period due to increasing effective nuclear charge. No anomalous increase at Group 15.
		* **Electron gain enthalpy:** Generally becomes more negative (increases in magnitude) across a period.  However, Group 15 elements show a less negative (smaller magnitude) electron gain enthalpy compared to Group 16 due to their half-filled $p$ subshells. This half-filled configuration provides extra stability, making it less favorable to add an electron.
 3. Determine the correct option:
  Result: Electron gain enthalpy shows the described anomalous behavior.
  Verification: The half-filled p-subshell in Group 15 elements makes it less favorable to add an electron compared to Group 16 elements.
 ## OPTION ANALYSIS
A :x: Ionization enthalpy increases across a period.
B :x: Atomic radius decreases across a period.
C :x: Electronegativity increases across a period.
D ✓: Electron gain enthalpy generally increases (becomes more negative) across a period, but Group 15 elements show an anomalous increase compared to Group 14 and 16 due to the stability of the half-filled $p$ subshell.  This means the magnitude of the electron gain enthalpy is less negative for Group 15.
 ## LEARNING AIDS
 **Common Mistakes**:
  1.Confusing electron gain enthalpy with ionization enthalpy: Remember that ionization enthalpy is the energy required to remove an electron, while electron gain enthalpy is the energy change when an electron is added.
  2.Ignoring the stability of half-filled and fully-filled subshells: The stability of these configurations significantly influences the periodic trends.
 **Quick Tips**:
  1.Visualize the periodic table and the trends of each property.
  2.Remember the half-filled and fully-filled subshell stability rule.

Mr. S M HUSSAIN · Answer

Ionization enthalpy

Mr. S M HUSSAIN · Answer

Atomic radius

Mr. S M HUSSAIN · Answer

Electronegativity

Mr. S M HUSSAIN · Answer

The correct Option is "Electron gain enthalpy"

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