ICSE Class 10 Chemistry: Periodic Table — Complete Notes 2026

History and Mendeleev's Periodic Law

• Mendeleev arranged 63 elements by increasing atomic mass; recurring properties
• Gaps for undiscovered elements (gallium, germanium) — predictions verified
• Anomalies in Mendeleev's table: argon-potassium, cobalt-nickel pairs

Modern Periodic Law and Table Structure

• Moseley: properties are periodic function of atomic number
• 18 groups (vertical columns) and 7 periods (horizontal rows)
• Blocks: s-block (groups 1–2), p-block (13–18), d-block (3–12), f-block (lanthanides, actinides)

Periodic Trends — Atomic Radius

• Atomic radius decreases across a period (increasing nuclear charge pulls electrons closer)
• Atomic radius increases down a group (new electron shells added)
• Covalent radius, van der Waals radius and ionic radius comparisons

Ionisation Energy

• Energy required to remove outermost electron from gaseous atom
• Increases across period; decreases down group
• Exceptions: Be > B and N > O (due to fully filled / half-filled subshells)

Electron Affinity and Electronegativity

• Electron affinity: energy released when atom gains an electron
• Electronegativity (Pauling scale): F=4.0 highest; increases across period, decreases down group
• Trend used to predict bond type: ionic, covalent, polar covalent

Valency and Metallic Character

• Valency pattern across period: 1,2,3,4,3,2,1,0
• Metallic character decreases across period; increases down group
• Non-metallic character: highest for halogens (group 17)

ICSE Exam Questions on Periodic Table

• Identify element given electron configuration and position in periodic table
• Explain why Na is more reactive than Mg
• State and explain why Cl has higher EA than S