Chemical Bonding and Molecular Structure –Detailed Notes (NCERT)

-

1. Introduction

  • Atoms combine to achieve stability (usually noble gas configuration).

  • Chemical bonds form due to lowering of potential energy when atoms come closer.

2. Types of Chemical Bonds

(A) Ionic Bond (Electrovalent bond)

  • Formed by complete transfer of electrons from one atom to another.

  • Example: NaCl (Na → Na⁺ + e⁻, Cl + e⁻ → Cl⁻).

  • Characteristics: hard, brittle, high melting point, conduct electricity in molten/aqueous state.

(B) Covalent Bond

  • Formed by mutual sharing of electron pairs.

  • Example: H₂, O₂, CH₄.

  • Can be single, double, triple depending on number of shared pairs.

(C) Coordinate (Dative) Bond

  • Shared pair of electrons contributed by only one atom.

  • Example: NH₄⁺, BF₃·NH₃.

(D) Hydrogen Bond

  • Weak bond formed between hydrogen (bonded to N, O, F) and a strongly electronegative atom.

  • Example: H₂O, HF, DNA base pairing.

  • Types:

    • Intermolecular (between molecules, as in H₂O).

    • Intramolecular (within same molecule, as in o-nitrophenol).

(E) Metallic Bond

  • Bond between metal atoms due to sea of delocalised electrons.

  • Explains properties like malleability, ductility, conductivity.

3. Theories of Chemical Bonding

(A) Octet Rule

  • Atoms tend to have 8 electrons in outer shell for stability.

  • Limitations: does not explain stability of odd-electron molecules (NO), incomplete octet (BF₃), expanded octet (SF₆).

(B) Lewis Structures

  • Represent valence electrons as dots and crosses.

  • Used to predict shape and stability of molecules.

(C) Valence Bond Theory (VBT)

  • Covalent bond formed by overlap of half-filled orbitals.

  • Types of overlap:

    • s–s, s–p, p–p overlap.

  • Sigma (σ) bond: head-on overlap.

  • Pi (π) bond: sideways overlap.

  • Explains directional nature of bonds.

(D) Hybridisation (Paulings concept)

  • Mixing of atomic orbitals to form new equivalent hybrid orbitals.

TypeOrbitals mixedGeometry Example
sp1s + 1pLinear (180°) BeCl₂
sp²1s + 2pTrigonal planar (120°) BF₃
sp³1s + 3pTetrahedral (109.5°) CH₄
sp³d1s + 3p + 1dTrigonal bipyramidal PCl₅
sp³d²1s + 3p + 2dOctahedral SF₆

Location: India

Comments

Post a Comment

Popular posts from this blog

Electrophilic and Nucleophilic Substitution Reactions – Detailed Notes & Mind Map

-
Image
    1. Definition of Substitution Reactions A Substitution Reaction is a type of chemical reaction in which one functional group in a molecule is replaced by another functional group or atom. 2. Electrophilic Substitution Reaction (ESR)   Definition: An Electrophilic Substitution Reaction is a chemical reaction where an electrophile (E⁺) replaces a hydrogen atom in an aromatic compound (most commonly benzene and its derivatives). General Reaction: Aromatic Compound (Ar–H) + E⁺ → Ar–E + H⁺ Mechanism of Electrophilic Aromatic Substitution (EAS): Example: Nitration of Benzene Step 1 – Generation of Electrophile (NO₂⁺): H N O 3 + H 2 S O 4 → N O 2 + + H S O 4 − + H 2 O HNO₃ + H₂SO₄ → NO₂^+ + HSO₄^- + H₂O Step 2 – Formation of Arenium Ion (σ-complex): Electrophile (NO₂⁺) attacks benzene → forms carbocation intermediate. Step 3 – Rearomatization: Loss of a proton (H⁺) restores aromaticity and produces nitrobenzene. Example Reactions: Nitration: Benzene +...
Read more

Classification of Elements and Periodicity in Properties

-
Classification of Elements and Periodicity in Properties July 29, 2024   by  Shivbalak Tiwari The classification of elements and the periodicity in their properties are foundational concepts in chemistry, encapsulated in the periodic table of elements. Here’s an overview: Classification of Elements Metals, Nonmetals, and Metalloids : Metals : Generally located on the left side and in the center of the periodic table. They are shiny, conductive, malleable, and ductile. Examples include iron, gold, and copper. Nonmetals : Found on the right side of the periodic table. They are usually not conductive, brittle in solid form, and have more varied physical properties. Examples include oxygen, sulfur, and chlorine. Metalloids : Located along the zigzag line (staircase) on the periodic table. They have properties intermediate between metals and nonmetals. Examples include silicon and arsenic. Groups and Periods : Groups : Vertical columns in the periodic table. Elements in the same gr...
Read more

Derivation of the Integrated Rate Law for a First-Order Reaction

-
Derivation of the Integrated Rate Law for a First-Order Reaction A first-order reaction is one where the rate of reaction depends linearly on the concentration of one reactant. The general form of a first-order reaction is: A → Products A → Products The rate of the reaction can be expressed as: Rate = − d [ A ] d t = k [ A ] Rate = − d t d [ A ] ​ = k [ A ] where: [ A ] [ A ]  is the concentration of the reactant  A A  at time  t t , k k  is the rate constant of the reaction. To derive the integrated rate law, we rearrange the equation to separate variables: d [ A ] [ A ] = − k   d t [ A ] d [ A ] ​ = − k d t Now, integrate both sides. The left side is integrated with respect to  [ A ] [ A ] , and the right side with respect to  t t : ∫ d [ A ] [ A ] = − ∫ k   d t ∫ [ A ] d [ A ] ​ = − ∫ k d t This gives: ln ⁡ [ A ] = − k t + C ln [ A ] = − k t + C where  C C  is the integration constant. To determine  C C , we use the initial condition ...
Read more