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Classification of Elements and Periodicity in Properties appeared 36 times across 3 years — 4.2% of Chemistry. This question is from Atomic Radii Trends.

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In period 4 of the periodic table, the elements with highest and lowest atomic radii are respectively.

Solution & Explanation

Core Logic

Period 4 runs from Potassium (K, Group 1) to Krypton (Kr, Group 18). Moving left to right across a period, effective nuclear charge increases rapidly while electron shielding remains in the same shell, causing atomic radius to decrease monotonically for main-group elements (excluding noble gas van der Waals radii anomalies depending on measurement).

Step 1: Identifying Extremes

Highest atomic radius: Alkali metal at the extreme left arrow Potassium (K). Lowest atomic radius (covalent): Halogen at the extreme right arrow Bromine (Br).

Pattern Recognition

The alkali metal always holds the largest atomic radius in any respective period. The halogen represents the minimum covalent radius.

Chapter Mix

Class 11 Chemistry: Classification of Elements and Periodicity in Properties

Reference Study Guides

Classification Of Elements And Periodicity In Properties

More Classification of Elements and Periodicity in Properties Previous-Year Questions — Page 8

Q70 jee_main_2024_31_jan_morning Electron Gain Enthalpy
The correct sequence of electron gain enthalpy of the elements listed below is A. Ar B. Br C. F D. S Choose the most appropriate from the options given below:
  • A. C > B > D > A
  • B. A > D > B > C
  • C. A > D > C > B
  • D. D > C > B > A

Solution

Core Logic

Electron gain enthalpy (ΔegH) values are considered with their signs when ordering from largest to smallest algebraically.

ElementΔegH (kJ/mol)
F-333
S-200
Br-325
Ar+96

Arranging these algebraically from highest to lowest: +96 > -200 > -325 > -333 Thus, Ar > S > Br > F, which corresponds to A > D > B > C.

Pattern Recognition

Noble gases always have positive electron gain enthalpies (highest algebraically). Halogens have highly negative values (lowest algebraically). Fluorine is highly negative, Bromine is slightly less negative. Sulfur sits in between.

Chapter Mix

Class 11 Chemistry: Classification of Elements and Periodicity in Properties

More Classification of Elements and Periodicity in Properties Questions — jee_main_2026_28_january_morning

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JEE Physics: Waves (+15.5%) | Electrostatics: Concentric Shells (-29.7%) | Modern Physics: Photoelectric Clones (+34.2%) | Mathematics: Definite Integrals (+18.1%) | Chemistry: Coordination Splitting (-11.4%) | JEE Physics: Waves (+15.5%) | Electrostatics: Concentric Shells (-29.7%) | Modern Physics: Photoelectric Clones (+34.2%) | Mathematics: Definite Integrals (+18.1%) | Chemistry: Coordination Splitting (-11.4%)