Chemical Bonding and Molecular Structure

Valence Bond Theory and Hybridisation

Valence Bond Theory :
Covalent bond is formed by the overlapping of half filled atomic orbitals.

 σ - bond π  - bond
 1. Strong bond 1. Weak bond
 2. Linear overlapping  2. Side wise overlapping
 3. Can exist independently  3. Can't exist independently
 4. Free rotation  4. no free rotation


As the size of orbital increases extent of overlapping decreases there by bond strength decreases
H — F > H — Cl > H — Br > H — I
Nuclear charge increases extent of overlap increases

Draw backs :

It failed to explain

  • Molecular geometry
  • Bond angles

Hybridization :
The intermixing of atomic orbitals of same atom having nearly same energy to produce an equivalent number of hybrid orbitals having identical shapes and energy is called hybridization.

Rules :
→ orbitals undergo hybridization but not electrons
→ Same atom only undergo hybridization
→ Angle is same between two hybrid orbitals

s–p hybridization :

sp2 – hybridization :

sp3 – hybridization :
Intermixing of 1s and 3p orbitals (px, py, pz)

sp3d – hybridization :
\% \ s \ - \ character - \frac{1}{5} \times 100 = 20 \%
\% \ p \ - \ character - \frac{3}{5} \times 100 = 60 \%
\% \ d \ - \ character - \frac{1}{5} \times 100 = 20 \%
% s character increases electronegativity increases

sp3d2 (or) d2sp3 hybridization :

Strong field ligands form d2sp3 or dsp3
Weak field ligands form sp3d2 (or) sp3d hybridization

View the Topic in this Video from 4:58 to 1:00:20

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