Carbon’s Tetravalence and Molecular Shapes

🔑 Key Concepts for NEET

  • Hybridization types (sp³, sp², sp) determine molecular shapes
  • π bonds create reactive sites and restrict rotation in double bonds
  • Higher s-character in hybrid orbitals = stronger bonds + higher electronegativity
  • Counting σ and π bonds in organic molecules
  • Predicting carbon hybridization in functional groups

💎 Why Carbon is Special

Carbon always forms 4 covalent bonds (tetravalence)! This shapes all organic molecules. Remember:

  • Methane (CH4) → Carbon uses sp³ orbitals → Tetrahedral shape
  • Ethene (C2H4) → Carbon uses sp² orbitals → Planar shape
  • Ethyne (C2H2) → Carbon uses sp orbitals → Linear shape

⚡ Hybridization Controls Bond Strength

Mixing s and p orbitals (hybridization) changes bond properties:

Hybrid Orbitals-characterBond LengthBond Strength
sp (e.g., C≡C)50%Shortest 🔥Strongest 💪
sp² (e.g., C=C)33%MediumMedium
sp³ (e.g., C-C)25%LongestWeakest

More s-character = orbitals closer to nucleus → stronger/shorter bonds!

🧲 Hybridization Affects Electronegativity

Higher s-character makes carbon more electronegative:

sp (50% s) > sp² (33% s) > sp³ (25% s)

This influences how carbon interacts with other atoms!

🔄 π Bonds: The Reactive Sites

Double/triple bonds contain π bonds with special features:

  • Formed by sideways overlap of p-orbitals
  • Require atoms to be in same plane 📐
  • Prevent rotation around double bonds (locked shape!)
  • Electron cloud above/below bond plane → super reactive!

π bonds are attack hotspots in molecules!

✏️ Practice Problems

Problem 1: Count σ and π bonds

(a) HC≡C–CH=CH–CH3
Solution: σC-C: 4, σC-H: 6, πC≡C: 2, πC=C: 1 → Total π bonds = 3

(b) CH2=C=CH–CH3
Solution: σC-C: 3, σC-H: 6, π bonds: 2

Problem 2: Find carbon hybridization

(a) CH3Cl → sp³ (single bonds)
(b) (CH3)2C=O → sp³ (CH3), sp² (C=O)
(c) CH3–C≡N → sp³ (CH3), sp (–C≡N)
(d) HCONH2 → sp² (carbonyl carbon)
(e) CH3–CH=CH–C≡N → sp³, sp², sp², sp

Problem 3: Hybridization and shape

(a) H2C=O → sp² hybridized → Trigonal planar
(b) CH3F → sp³ hybridized → Tetrahedral
(c) HC≡N → sp hybridized → Linear

💡 Remember This!

Carbon’s 4-bond superpower comes from s+p orbital mixing. This controls shape, bond strength, and reactivity – the foundation of organic chemistry! 🧪