Valence Bond Theory and Hybridisation

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

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 (p_x, p_y, p_z)

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