Periodic Table and Element Classification

Sep 9, 2024

Chemistry Lecture Notes: Classification of Elements and Periodicity in Properties

Overview

  • This lecture is part of the Class 11 Chemistry series.
  • Focus on the Chapter: Classification of Elements and Periodicity in Properties.
  • Importance of understanding the periodic table for dealing with subsequent chemistry chapters.

Key Concepts

Periodic Table History

  • Number of Elements: Approximately 120 elements are known, with some artificially made.
  • The periodic table organizes these elements in a structured pattern, facilitating the study of chemistry.
  • Modern Periodic Table: The current standard, developed after many iterations.

Historical Periodic Tables

  1. Dobereiner's Law of Triads

    • Based on atomic mass.
    • Elements grouped in triads (e.g., Li, Na, K); middle element's atomic mass is the average of the first and third.
    • Limitation: Could only organize a few elements.

  2. Newlands' Law of Octaves

    • Arranged by increasing atomic mass.
    • Every eighth element has similar properties to the first.
    • Limitation: Applicable only till calcium; two elements were placed in a single slot.

  3. Lothar Meyer's Periodic Table

    • Graph plotted between atomic volume (density) and atomic mass.
    • Elements positioned in the graph indicating similar properties (peaks: alkali metals; descending curve: alkaline earth metals).
    • Limitation: Not all elements with similar properties fit the curve pattern.

  4. Mendeleev's Periodic Table

    • Elements arranged by atomic mass.
    • Introduced the concept of groups (vertical columns) and periods (horizontal rows).
    • Left gaps for undiscovered elements, accurately predicted properties and positions of several elements.
    • Mendeleev's Periodic Law: Physical and chemical properties are periodic functions of atomic masses.
    • Limitations include uncertain position for hydrogen, no position for isotopes, and some misplaced elements (e.g., Tellurium & Iodine).

Modern Periodic Table

  • Developed from previous efforts, addressing their limitations.
  • Analysis of modern periodic table will be covered in subsequent classes.

Upcoming Topics

  • Detailed discussion on the modern periodic table.
  • Exploration of periodic properties such as atomic size, ionic size, ionization enthalpy, electronegativity, and valency.

Conclusion

  • Understanding the foundation and evolution of the periodic table is crucial for mastering chemistry.
  • The next class will cover the modern periodic table in depth.

This lecture provides a comprehensive overview of the historical development of the periodic table, paving the way for understanding modern chemical properties and classifications.