Chemical Bonding: Hybridization and Molecular Shapes

🔍 Sigma (σ) and Pi (π) Bonds

Sigma Bond (σ): Formed by end-to-end overlap of orbitals along the internuclear axis. Types:

• s-s overlapping: Two s-orbitals overlap
• s-p overlapping: s-orbital and p-orbital overlap
• p-p overlapping: Two p-orbitals overlap axially

Pi Bond (π): Formed by sideways overlap of p-orbitals. Orbitals stay parallel to each other and perpendicular to the internuclear axis.

💡 Key fact: Sigma bonds are stronger than pi bonds due to greater orbital overlap! Multiple bonds = 1 σ bond + π bond(s).

🌈 Hybridization: Mixing Atomic Orbitals

Atomic orbitals mix to form new hybrid orbitals with equal energy and shape. This explains molecular geometries!

Conditions for Hybridization:

• Only valence shell orbitals hybridize
• Orbitals must have similar energy
• Electron promotion isn’t always needed
• Filled orbitals can participate too!

🔷 Types of Hybridization

1. sp Hybridization (Linear Geometry)

• Mixing: 1 s + 1 p orbital → 2 sp hybrids
• Angle: 180°
• Example: BeCl₂
  • Be: 1s²2s² → excited state 2s¹2p¹
  • 2 sp hybrids form 2 σ bonds with Cl

2. sp² Hybridization (Trigonal Planar)

• Mixing: 1 s + 2 p orbitals → 3 sp² hybrids
• Angle: 120°
• Example: BCl₃
  • B: 1s²2s²2p¹ → excited state 2s¹2p²
  • 3 sp² hybrids form 3 σ bonds with Cl

3. sp³ Hybridization (Tetrahedral)

• Mixing: 1 s + 3 p orbitals → 4 sp³ hybrids
• Angle: 109.5°
• Examples:
  • CH₄: 4 sp³ orbitals form σ bonds with H
  • NH₃: 3 sp³ orbitals bond with H; 1 holds lone pair → bond angle 107° (pyramidal)
  • H₂O: 2 sp³ orbitals bond with H; 2 hold lone pairs → bond angle 104.5° (bent/V-shape)

⛓ Hybridization in Hydrocarbons

Ethane (C₂H₆): sp³ Hybridization

• Each C has 4 sp³ hybrids
• C-C bond: sp³-sp³ σ bond
• C-H bonds: sp³-s σ bonds

Ethene (C₂H₄): sp² Hybridization

• Each C has 3 sp² hybrids + 1 unhybridized p-orbital
• C-C bond: 1 sp²-sp² σ bond + 1 p-p π bond
• C-H bonds: sp²-s σ bonds

Ethyne (C₂H₂): sp Hybridization

• Each C has 2 sp hybrids + 2 unhybridized p-orbitals
• C-C bond: 1 sp-sp σ bond + 2 p-p π bonds (triple bond!)
• C-H bonds: sp-s σ bonds

📐 Hybridization with d-Orbitals

PCl₅: sp³d Hybridization

• Geometry: Trigonal bipyramidal
• P orbitals: 1s + 3p + 1d hybridize → 5 sp³d orbitals
• Bond angles: 120° (equatorial), 90° (axial)
• Axial bonds longer/weaker than equatorial bonds!

SF₆: sp³d² Hybridization

• Geometry: Octahedral
• S orbitals: 1s + 3p + 2d hybridize → 6 sp³d² orbitals
• All bond angles = 90°

🚀 NEET Must-Knows!

1. Geometry & Hybridization:
   • sp → Linear (180°)
   • sp² → Trigonal planar (120°)
   • sp³ → Tetrahedral (109.5°)
   • sp³d → Trigonal bipyramidal
   • sp³d² → Octahedral
2. Lone Pairs Change Angles:
   • NH₃: 107° (lone pair repulsion)
   • H₂O: 104.5° (two lone pairs)
3. Sigma vs. Pi Bonds:
   • Single bond: 1 σ
   • Double bond: 1 σ + 1 π
   • Triple bond: 1 σ + 2 π
4. Carbon Compounds:
   • C₂H₆ (sp³), C₂H₄ (sp² + π bond), C₂H₂ (sp + 2π bonds)
5. d-Orbital Hybridization: PCl₅ (sp³d), SF₆ (sp³d²)

💎 Final Tip

Hybridization = Mix-and-match orbitals to fit electron pairs! Lone pairs take space and squish bond angles. 😊