Lecture Notes: Periodic Classification of Elements

Introduction

• Periodic Classification: Understanding elements and their properties.
• Historical context: Changes in element table over the years.
• Concept of focusing on goals, similar to Arjun in Mahabharata.

Chapter Overview

• Classification of Elements and Periodic Properties.
• Importance of periodic properties in 11th and 12th class chemistry.

Historical Development of Periodic Table

Early Classification

• Negishi's Classification: Divided elements into metals and non-metals.
• Issues arose with metalloids that exhibit properties of both.
• Döbereiner's Triads: Grouped elements in threes based on atomic mass and chemical properties.

Newland's Octaves

• Arranged elements in increasing atomic mass with similar properties every eighth element.
• Challenges with the discovery of noble gases.

Mendeleev's Table

• Systematic classification based on atomic weight.
• Recognition of periodicity in chemical properties.
• Limitations: Hindered by the discovery of new elements and isotopes.

Modern Periodic Table

• Basis on Atomic Number: Modern table organized by atomic number.
• Elements divided into blocks: s, p, d, f blocks.
  • s-block: Group 1 & 2 (Alkali and Alkaline Earth Metals).
  • p-block: Group 13 to 18.
  • d-block: Transition metals (Groups 3 to 12).
  • f-block: Lanthanides and Actinides.

Key Concepts in Atomic Structure

Atomic Radius

• Distance from nucleus to outermost electron shell.
• Factors affecting atomic size:
  • Atomic Size: Larger atomic size results in lower ionization energy.
  • Nuclear Charge: Higher positive charge reduces atomic size.
  • Shielding Effect: Inner electrons repel outer electrons, increasing size.

Ionization Energy

• Energy required to remove an electron from an isolated atom.
• Trends:
  • Increases across a period and decreases down a group.
  • Factors influencing ionization energy include:
    • Atomic Size: Larger size leads to lower ionization energy.
    • Nuclear Charge: Stronger attraction means higher ionization energy.
    • Penetration Effect: Electrons in lower energy levels shield outer electrons.
    • Electron Configuration Stability: Half-filled and fully filled configurations have higher stability.

Electron Affinity

• Energy change when an electron is added to an atom.
• Exothermic process for some elements, typically halogens.

Questions & Practice

• Engage with previous years’ questions to test understanding.
• Emphasize understanding the exceptions in periodic trends.

Conclusion

• Importance of understanding periodic properties in chemistry.
• Continuously revise and practice for better retention.