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:
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History and Development
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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.
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Newlands’ Law of Octaves: Every eighth element showed similar properties when arranged by increasing atomic mass.
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Mendeleev’s Periodic Table: Arranged elements by increasing atomic mass; left gaps for undiscovered elements.
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Modern Periodic Law (Moseley): Properties of elements are a periodic function of their atomic number (not mass).
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Structure of the Modern Periodic Table
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Periods: Horizontal rows (7 in total).
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Groups: Vertical columns (18 in total).
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Elements are arranged based on increasing atomic number.
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Classification of Elements
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Metals, Nonmetals, and Metalloids.
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Representative elements (Groups 1, 2, 13–18), Transition elements (Groups 3–12), and Inner transition elements (Lanthanides and Actinides).
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Groups and Their Characteristics
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Group 1 (Alkali metals): Highly reactive, soft metals.
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Group 2 (Alkaline earth metals): Reactive metals, less so than Group 1.
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Group 17 (Halogens): Very reactive nonmetals.
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Group 18 (Noble gases): Inert gases with full outer shells.
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Periodic Trends
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Atomic Radius: Decreases across a period, increases down a group.
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Ionisation Energy: Increases across a period, decreases down a group.
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Electron Affinity & Electronegativity: Increase across a period, decrease down a group.
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Metallic character: Decreases across a period, increases down a group.
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Blocks of Elements
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Based on the type of orbital receiving the last electron:
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s-block: Groups 1 & 2
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p-block: Groups 13–18
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d-block: Transition metals
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f-block: Lanthanides & Actinides
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🔸 Importance of the Periodic Table
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Predicts element behaviour.
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Identifies trends in chemical reactivity and bonding.
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Serves as a foundational tool for understanding chemical properties and reactions.