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:
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).
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.
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).
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.
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.
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.