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Classification of Elements and Periodicity in Properties — Revision Notes

NEET-UG · Chemistry

Free Classification of Elements and Periodicity in Properties revision notes for NEET-UG Chemistry 2026 — key concepts, formulas, and definitions for quick revision.

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A diagram illustrating Dobereiner's Triads, showing three elements with similar properties, where the atomic weight of the middle element is approximately the arithmetic mean of the other two. Example
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Revision Notes — Classification of Elements and Periodicity in Properties

Key concepts, formulas, and definitions from Classification of Elements and Periodicity in Properties for NEET-UG Chemistry preparation.

Key Topics to Revise

1

Evolution of Periodic Classification

  • Dobereiner's Triads: Elements arranged in groups of three with middle element's atomic weight as arithmetic mean of other two (Li-7, Na-23, K-39)
  • Newland's Octave Law: Every eighth element had similar properties when arranged by increasing atomic weight
  • Mendeleev's Periodic Law: Properties are periodic functions of atomic weights
2

Modern Periodic Table Structure

  • 18 vertical groups (1-18) and 7 horizontal periods
  • s-block: Groups 1-2 (alkali and alkaline earth metals)
  • p-block: Groups 13-18 (metalloids, non-metals, noble gases)
3

Atomic and Ionic Radii

  • Atomic radius decreases across period due to increasing nuclear charge
  • Atomic radius increases down group due to addition of electron shells
  • Covalent radius = half of internuclear distance in covalent bond
4

Ionization Energy and Electron Affinity

  • IE increases across period (with exceptions for Group 2→3 and Group 5→6)
  • IE decreases down group due to increased atomic size and shielding
  • IE₁ < IE₂ < IE₃ due to increased effective nuclear charge

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Key Concepts

States that 'The properties of elementsElements are classified into four blocksAtomic radius decreases across a periodEnergy required to remove the outermostEnergy released when an electron

Frequently Asked Questions

What topics are covered in Classification of Elements and Periodicity in Properties for NEET-UG?
Classification of Elements and Periodicity in Properties is an important chapter in NEET-UG Chemistry. It covers key concepts and formulas that are frequently tested in the exam. Key topics include: Evolution of Periodic Classification, Modern Periodic Table Structure, Atomic and Ionic Radii, Ionization Energy and Electron Affinity.
How important is Classification of Elements and Periodicity in Properties for NEET-UG?
Classification of Elements and Periodicity in Properties is a frequently tested chapter in NEET-UG Chemistry. Questions from this chapter appear regularly in previous year papers. There are 58 practice questions available for this chapter.
How to prepare Classification of Elements and Periodicity in Properties for NEET-UG?
Start by understanding the core concepts, then solve practice questions. Focus on formulas and their applications. Use revision notes for quick review before the exam.

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