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Resonance Chemistry Chemical Bonding

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 CHEMICAL BONDING - Resonance Chemistry Notes

Chemical bonding is one of the most important topics in Physical Chemistry for JEE, NEET, and GATE. It explains how atoms combine to form molecules through various types of forces.

 1. Types of Chemical Bonds

Bond Type How It Forms? Example
Ionic Bond Transfer of electrons NaCl, KCl, MgO
Covalent Bond Sharing of electrons H₂, O₂, CH₄
Coordinate Bond One atom donates a lone pair NH₃ → BF₃, H₃O⁺
Metallic Bond Delocalized electron cloud Cu, Fe, Ag
Hydrogen Bond H atom bonded to F, O, N H₂O, NH₃, HF

 2. Octet Rule & Its Limitations

Octet Rule → Atoms tend to gain, lose, or share electrons to complete 8 valence electrons (stable noble gas configuration).
Limitations:
 Incomplete Octet: BeCl₂, BCl₃
 Expanded Octet: SF₆, PCl₅
 Odd Electron Species: NO, NO₂

 3. Valence Bond Theory (VBT) & Hybridization

 VBT: Explains bonding in terms of atomic orbitals overlapping to form bonds.
 Hybridization: Mixing of orbitals to form new hybrid orbitals of equal energy.

Hybridization Shape Example
sp Linear (180°) BeCl₂, CO₂
sp² Trigonal Planar (120°) BF₃, SO₃
sp³ Tetrahedral (109.5°) CH₄, NH₃, H₂O
sp³d Trigonal Bipyramidal (90°, 120°) PCl₅
sp³d² Octahedral (90°) SF₆, [Ni(CN)₄]²⁻

 4. Molecular Orbital Theory (MOT)

 Atomic orbitals combine to form Molecular Orbitals (MO).
Bond Order = (Bonding e⁻ - Antibonding e⁻) / 2
 Higher bond order → Stronger bond & shorter bond length.

MOT Order for O₂, F₂, etc.:
σ(1s) < σ*(1s) < σ(2s) < σ*(2s) < π(2px) = π(2py) < σ(2pz) < π(2px) = π(2py)** < σ*(2pz)

Paramagnetic molecules: O₂, B₂ (Unpaired e⁻)
Diamagnetic molecules: N₂, F₂ (All paired e⁻)

 5. Dipole Moment (μ) and Bond Polarity

μ = Charge (q) × Bond Length (d)
Polar molecules: H₂O, NH₃, HF (μ ≠ 0)
Nonpolar molecules: CO₂, BF₃, CH₄ (μ = 0)

 6. Resonance & Formal Charge

Resonance: Delocalization of π-electrons, stabilizing the molecule.
Example:
 Ozone (O₃)
 Benzene (C₆H₆)
 Carbonate ion (CO₃²⁻)

Formal Charge = (Valence e⁻ - Nonbonding e⁻ - Bonding e⁻/2)
Used to determine the most stable resonance structure.

 Tips for JEE/NEET/GATE

Remember hybridization rules (sp, sp², sp³)
MOT diagrams are important for O₂, N₂, F₂
Practice bond order and dipole moment questions
Know the exceptions of the octet rule

 Do you need solved examples or short tricks for Chemical Bonding?

Resonance Chemistry Chemical Bonding

(968)-chemistry-gyan-sutra-jee-main.pdf

CHEMiCAL BOnDinG AnD MOLECULAR StRUCtURE

Resonance in Chemistry is a key concept in chemical bonding, especially in the context of molecular structure and stability. It is commonly asked in GATE and other competitive exams. Here's a quick breakdown:

What is Resonance?

Resonance refers to the delocalization of electrons within molecules that have conjugated double bonds or lone pairs next to π bonds. Instead of existing in a single Lewis structure, such molecules are best represented by multiple resonance structures.

These structures differ only in the arrangement of electrons, not in the position of atoms.

Key Characteristics of Resonance:

  1. Real structure is a hybrid: The actual structure is a resonance hybrid, more stable than any single contributing structure.

  2. Resonance energy: The difference in energy between the most stable resonance structure and the hybrid.

  3. Stabilization: Resonance increases molecular stability.

  4. No real shifting: Electrons don’t actually move back and forth—they are delocalized.

Example: Benzene C6H6C_6H_6

  • Has two equivalent resonance structures:

    Structure 1:                                      \text{Structure 1: } \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ Alternating single and double bonds\text{Alternating single and double bonds} Structure 2:   Double and single bonds reversed\text{Structure 2: } \ \ \text{Double and single bonds reversed}

  • Actual structure: All C–C bonds are equal in length due to π-electron delocalization.

Rules for Drawing Resonance Structures:

  1. Same molecular formula and position of atoms.

  2. Only π electrons or lone pairs can move.

  3. Octet rule must be obeyed (especially for 2nd period elements).

  4. Overall charge must remain the same.

Common Compounds Showing Resonance:

  • Ozone (O₃)

  • Nitrate ion (NO₃⁻)

  • Carbonate ion (CO₃²⁻)

  • Acetate ion (CH₃COO⁻)

Importance in GATE Chemistry:

  • Predicting molecular geometry (via hybridization and resonance).

  • Calculating formal charge and stability.

  • Understanding acid-base behavior and reactivity.

Let me know if you'd like a diagram of resonance structures, practice GATE questions, or a video explanation to reinforce this topic.

Resonance Chemistry Chemical Bonding

Unit: 8 Chemical Bonding: Resonance