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Classification of Elements and Periodicity in Properties

CBSE · Class 11 · Chemistry

Quick revision notes for Classification of Elements and Periodicity in Properties — CBSE Class 11 Chemistry. Key concepts, formulas, and definitions for last-minute revision.

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Key Topics to Revise

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1. Need for Classification and Historical Development

  • In 1800 only 31 elements were known; by 1865 this number had more than doubled to 63; at present 114 elements are known.
  • A large number of elements made individual study difficult, so classification helped organize knowledge and predict new facts.
  • Johann Dobereiner identified Triads in the early 1800s. In each triad, the middle element had an atomic weight about halfway between the other two and also showed intermediate properties.
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2. Modern Periodic Table: Periods, Groups, and Nomenclature

  • The modern periodic table is the long form of the periodic table and is based on atomic number.
  • There are seven periods and eighteen groups.
  • The period number corresponds to the highest principal quantum number of the elements in that period.
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3. Electronic Configuration and Block Classification

  • The position of an element in the periodic table reflects the electronic configuration of the last filled orbital.
  • Elements are classified into s-block, p-block, d-block, and f-block according to the orbital being filled.
  • The s-block contains Groups 1 and 2.
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4. Periodic Trends in Atomic and Ionic Radii

  • Atomic radius is estimated from interatomic distances because an atom has no sharp boundary.
  • For non-metals, covalent radius is taken as half the bond distance in a covalent molecule.
  • For metals, metallic radius is half the internuclear distance in the metallic crystal.

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Full Notes

Key Concepts

Dobereiner grouped elements into triadsMendeleev stated that the propertiesMoseley showed through XThere are seven periodsElements are classified into s

Frequently Asked Questions

What are the important topics in Classification of Elements and Periodicity in Properties for CBSE Class 11 Chemistry?
Classification of Elements and Periodicity in Properties covers several key topics that are frequently asked in CBSE Class 11 board exams. Focus on the core concepts listed on this page and practise related questions to build confidence.
How to score full marks in Classification of Elements and Periodicity in Properties — CBSE Class 11 Chemistry?
Understand the core concepts first, then work through the 77 practice questions available for this chapter. Revise formulas and definitions regularly, and use flashcards for quick recall before the exam.

Sources & Official References

Content is aligned to the official syllabus. Refer to the board website for the latest curriculum.

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