Hybridization & Molecular Geometry

CompleteFundamentals of Chemistry

Mixing of atomic orbitals to produce new equivalent orbitals that explain molecular shape.

Full notes

Definition: Hybridization is the mixing of atomic orbitals of nearly equal energy on the same atom to give an equal number of new, equivalent hybrid orbitals that point in specific directions.

1. Common hybridizations

sp: linear, 180° — BeCl₂, C in C≡C
sp²: trigonal planar, 120° — BF₃, ethylene
sp³: tetrahedral, 109.5° — CH₄, NH₃(lone pair), H₂O(lone pairs)
sp³d: trigonal bipyramidal — PCl₅
sp³d²: octahedral — SF₆

2. Lone pairs shrink the angle

An sp³ center with a lone pair: CH₄ 109.5°, NH₃ 107°, H₂O 104.5°. Lone pairs occupy more space (they are held by only one nucleus), so they compress the bond angle.

3. Bent's rule

Bent's rule: in a molecule, atomic orbitals with higher s-character concentrate on electropositive substituents; more electronegative substituents bond with orbitals of higher p-character. Example: in PF₃Cl₂, Cl (more electronegative) occupies axial positions (p-orbital character higher), F occupies equatorial (more s-character).

Hybridization	Shape	Angle	Example
sp	Linear	180°	BeCl₂, CO₂
sp²	Trigonal planar	120°	BF₃, C₂H₄
sp³	Tetrahedral	109.5°	CH₄
sp³d	Trigonal bipyramidal	90°/120°	PCl₅
sp³d²	Octahedral	90°	SF₆

Note: Exam point: prediction method — count σ bonds + lone pairs = hybrid index. 2→sp, 3→sp², 4→sp³, 5→sp³d, 6→sp³d².

Exam notes

Hybrid index = number of σ bonds + number of lone pairs. Geometry follows from hybrid. Lone pair compresses angle.

Important points

Hybridization is a bookkeeping device of VBT — it predicts geometry, not electronic reality.

Common mistakes

Counting π bonds in the hybrid index — π bonds are NOT counted.

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