Chapter: Chemical Bonding, Class 11
Study Notes
Covalent Bond
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Covalent Bond – Lecture Notes
Class 11 | Chemistry
Definition
A covalent bond is sharing of electrons between atoms to achieve stable electronic configuration.
Types
Single, Double, Triple, Coordinate covalent bond.
Characteristics
Usually low melting and boiling points (except network solids), poor electrical conductivity, often soluble in non-polar solvents.
Classification based on Electronegativity
Non-polar covalent bond → negligible ΔEN (e.g., H₂, Cl₂, O₂).
Polar covalent bond → moderate ΔEN with partial charges (e.g., HCl, H₂O, NH₃).
Polar covalent bond → moderate ΔEN with partial charges (e.g., HCl, H₂O, NH₃).
Lewis Representation of Simple Molecules
Dot-and-cross structures for shared pairs (e.g., H₂O: two bonding pairs + two lone pairs on O).
Variable Covalency and Its Reason
Elements with vacant d-orbitals (P, S, Cl) can expand their octet and show multiple valencies (PCl₃ vs PCl₅, SF₆).
Formal Charge
FC = (Valence e⁻) − (Nonbonding e⁻ + ½ × Bonding e⁻); helps identify the most stable resonance structure.
Bond Parameters
Bond length → Triple < Double < Single.
Bond angle → CH₄ (109.5°) > NH₃ (107°) > H₂O (104.5°).
Bond enthalpy → Triple > Double > Single.
Bond order → Higher order means stronger, shorter bonds; resonance gives fractional.
Bond angle → CH₄ (109.5°) > NH₃ (107°) > H₂O (104.5°).
Bond enthalpy → Triple > Double > Single.
Bond order → Higher order means stronger, shorter bonds; resonance gives fractional.
Limitations of Octet Rule / Deviations
Incomplete octet (BeCl₂, BF₃).
Expanded octet (SF₆, PCl₅).
Odd-electron species (NO, NO₂).
Hypervalent / hypovalent molecules.
Expanded octet (SF₆, PCl₅).
Odd-electron species (NO, NO₂).
Hypervalent / hypovalent molecules.