Periodic Table

Summary Note: Periodic Table (NEB Grade 11 / Entrance Focused)

Periodic Table:

The Periodic Table is a systematic arrangement of chemical elements based on their atomic number, electron configuration, and recurring chemical properties. It helps predict the properties of elements and their compounds.

🔹 Key Concepts:

  1. History and Development

    • Dobereiner’s Triads: Groups of three elements with similar properties; the atomic mass of the middle element is nearly the average of the other two.

    • Newlands’ Law of Octaves: Every eighth element showed similar properties when arranged by increasing atomic mass.

    • Mendeleev’s Periodic Table: Arranged elements by increasing atomic mass; left gaps for undiscovered elements.

    • Modern Periodic Law (Moseley): Properties of elements are a periodic function of their atomic number (not mass).

  2. Structure of the Modern Periodic Table

    • Periods: Horizontal rows (7 in total).

    • Groups: Vertical columns (18 in total).

    • Elements are arranged based on increasing atomic number.

  3. Classification of Elements

    • Metals, Nonmetals, and Metalloids.

    • Representative elements (Groups 1, 2, 13–18), Transition elements (Groups 3–12), and Inner transition elements (Lanthanides and Actinides).

  4. Groups and Their Characteristics

    • Group 1 (Alkali metals): Highly reactive, soft metals.

    • Group 2 (Alkaline earth metals): Reactive metals, less so than Group 1.

    • Group 17 (Halogens): Very reactive nonmetals.

    • Group 18 (Noble gases): Inert gases with full outer shells.

  5. Periodic Trends

    • Atomic Radius: Decreases across a period, increases down a group.

    • Ionisation Energy: Increases across a period, decreases down a group.

    • Electron Affinity & Electronegativity: Increase across a period, decrease down a group.

    • Metallic character: Decreases across a period, increases down a group.

  6. Blocks of Elements

    • Based on the type of orbital receiving the last electron:

      • s-block: Groups 1 & 2

      • p-block: Groups 13–18

      • d-block: Transition metals

      • f-block: Lanthanides & Actinides

🔸 Importance of the Periodic Table

  • Predicts element behaviour.

  • Identifies trends in chemical reactivity and bonding.

  • Serves as a foundational tool for understanding chemical properties and reactions.

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