Periodic Table and Periodicity

1. Introduction

• Importance of systematic classification in libraries
• Systematic classification of chemical elements: The Periodic Table
• Facilitates location, identification, and characterization of elements

2. Genesis of Periodic Classification

2.1 Prout's Hypothesis

• Atomic weights as multiples of hydrogen
• Rejected due to fractional atomic weights

2.2 Döbereiner's Triads

• Classification in groups of three: Triads
• Merits: Focus on groups with similar properties
• Demerits: Inconsistencies in triads

2.3 Newlands' Rule of Octaves

• Elements arranged by increasing atomic weights
• Similar properties every eighth element
• Limited to about 20 elements, failed for heavier elements

2.4 Lothar Meyer's Volume Curves

• Atomic volumes vs atomic weights
• Different elements occupy maxima, midpoints, and minima on curves
• Limited practical utility

2.5 Mendeleev’s Periodic Law

• Elements' properties periodic functions of atomic weights
• Merits: Systematic study, prediction of elements, correction of atomic masses
• Limitations: Position issues with hydrogen, isotopes, metals, non-metals

2.6 Modern Periodic Law and Table

• Properties periodic functions of atomic numbers
• Structured in periods and groups
• Advantages: Correlation with electronic configuration, clear separation of elements
• Defects: Position of hydrogen, helium, f-block elements

3. Naming of Elements with Atomic Numbers > 100

• Derived from atomic numbers using numerical roots
• Symbols are initials of numerical roots

4. Classification Based on Blocks

• s-block Elements: Groups 1 & 2; soft, low melting points
• p-block Elements: Groups 13-18; diverse properties, higher ionization energies
• d-block Elements: Transition metals; hard, conductive, catalytic
• f-block Elements: Inner-transition elements; lanthanides and actinides

5. Metals, Non-Metals, and Metalloids

• Trends in metallic and non-metallic character in the periodic table

6. Effective Nuclear Charge and Shielding

• Shielding decreases effective nuclear charge
• Slater's rules for calculating shielding constants

7. Trends in Physical Properties

7.1 Atomic Radius

• Decreases across a period, increases down a group

7.2 Ionization Potential

• Energy to remove electrons; increases across a period, decreases down a group

7.3 Electron Affinity

• Energy change when an electron is added to a gas-phase atom
• Trends: Increases across a period, decreases down a group

7.4 Electronegativity

• Tendency to attract electrons, increases across periods, decreases down groups
• Measured using scales like Pauling and Mulliken

8. Trends in Chemical Properties

• Valency trends in groups and periods
• Periodic properties: Ionization, electron affinity, atomic/ionic radii, etc.

9. Important Points

• Notable elements: Francium, Astatine, Plutonium, Technetium
• Trends in melting points, densities, and other properties

• The periodic table organizes elements according to increasing atomic number, resulting in a gradual change in properties, which helps in understanding the behavior of elements in chemical reactions.
• The modern periodic table is a valuable tool for predicting chemical behavior and relationships between elements.