Are you a Class 11 FBISE student struggling with Chapter 3 Chemical Bonding Easy Notes: Electronegativity Trends (NBF) under the new National Book Foundation (NBF) curriculum? You’re not alone! Electronegativity trends are the foundation of understanding bond types, polarity, and molecular behavior. This solved notes guide breaks down every concept with crystal-clear explanations, solved exercises, trends, examples, and memory tricks — all aligned with FBISE new course, NBF, and Cantab standards.
Download the full PDF now for easy notes, complete solutions, diagrams, tables, and VSEPR predictions to ace your exams!
What is Electronegativity? (Solved Definition & Pauling Scale)
Electronegativity is defined as an atom’s ability to attract shared electrons in a chemical bond. It’s measured on the Pauling scale, where:
- Fluorine (F) = 4.0 → Highest electronegativity
- Francium (Fr) = 0.7 → Lowest electronegativity
Solved Example: Why is F the most electronegative?
Ans: Smallest atomic size + highest effective nuclear charge → strongest pull on bonding electrons.
Focus Keyword: Chapter 3 Chemical Bonding Easy Notes: Electronegativity Trends (NBF)
Electronegativity Trends in Periodic Table – Down the Group & Across the Period (Solved)
| Direction | Electronegativity Trend | Reason (Solved) |
|---|---|---|
| Down a Group (Top → Bottom) | Decreases | More electron shells → weaker nuclear pull on bonding electrons |
| Across a Period (Left → Right) | Increases | More protons + smaller atomic size → stronger pull on electrons |
Solved Trend Examples:
- Down Group 17: F > Cl > Br > I → Electronegativity decreases
- Across Period 3: Na < Mg < Al < Si < P < S < Cl → Electronegativity increases
Memory Trick:
- Groups: “Bigger atoms = Greedy but weak” (size wins)
- Periods: “Smaller and stronger” (tight pull)
Nature of Chemical Bonds Based on Electronegativity Difference (ΔEN) – Fully Solved
| ΔEN | Bond Type | Example | Explanation |
|---|---|---|---|
| 0 | Pure Covalent | O₂, Cl₂ | Equal sharing |
| 0.4 – 1.8 | Polar Covalent | HCl (ΔEN = 0.96) | Unequal sharing → partial charges |
| > 1.8 | Ionic | KCl (ΔEN = 2.34) | Electron transfer |
Solved Exercise 3.1 (From PDF – Concept Assessment)
| Molecule | ΔEN | Polarity | Reason (Solved) |
|---|---|---|---|
| Cl₂ | 3.0 – 3.0 = 0 | Non-polar | Same atoms, symmetrical |
| HF | 4.0 – 2.1 = 1.9 | Polar | Large ΔEN, linear |
| SCl₂ | 3.0 – 2.5 = 0.5 | Polar | Bent shape, dipoles don’t cancel |
| CHCl₃ | 3.0 – 2.5 = 0.5 | Polar | Tetrahedral but asymmetrical |
| CBr₄ | 2.8 – 2.5 = 0.3 | Non-polar | Symmetrical tetrahedral |
Download PDF for full solved table + diagrams!
Covalent Character in Ionic Compounds – Trend & Solved Example
- Higher oxidation state of cation → More covalent character
- Reason: Smaller, highly charged cation polarizes anion more → electron cloud distortion
Solved Example:
AlCl₃ (+3) is more covalent than MgCl₂ (+2)
Why? Al³⁺ is smaller and has higher charge → stronger polarizing power
Trend: Left → Right in period → Covalent character increases
Why Electronegativity Trends Matter? (Real-Life Applications)
- High ΔEN → Ionic bond → High melting point (e.g., NaCl)
- Moderate ΔEN → Polar molecules → Soluble in water (e.g., HCl, HF)
- Low ΔEN → Non-polar → Insoluble in water (e.g., oils)
One-Line Summary for Quick Revision
Down the group: Electronegativity decreases (bigger atoms)
Across the period: Electronegativity increases (stronger pull)
Why Download This PDF? (Benefits for Class 11 FBISE Students)
This Chapter 3 Chemical Bonding Easy Notes: Electronegativity Trends (NBF) PDF includes:
✅ Solved Concept Assessment Exercise 3.1
✅ Electronegativity trends with reasons & examples
✅ Bond type classification table (0, 0.4–1.8, >1.8)
✅ Polarity of molecules (Cl₂, HF, SCl₂, CHCl₃, CBr₄)
✅ Memory tricks, tables, diagrams
✅ Aligned with FBISE, NBF, Cantab new syllabus
✅ Perfect for board exams, entry tests, and quick revision
Download Now & Master Electronegativity Trends!
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📥 Download Chapter 3 Chemical Bonding Easy Notes: Electronegativity Trends (NBF) – Solved PDF
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