Hybridization

Hybridization – Study Notes

(Manipal MET – Chemistry)

1. Simple Explanation

Hybridization is a quantum‑mechanical model that explains the shape of molecules by mixing atomic orbitals (AOs) on the same atom to form new, equivalent hybrid orbitals.

• Why hybridize?
  • To account for the observed bond angles that cannot be explained by pure s or p orbitals alone.
  • To describe the spatial arrangement of bonds and lone pairs around a central atom.
• Conceptually: 1 s + 1 p → sp, 1 s + 2 p → sp², 1 s + 3 p → sp³, etc.
• Result: Each hybrid orbital contains equal portions of s and p (or d) character, leading to predictable geometries.

2. Key Points

Important Notes

1. Lone pairs occupy hybrid orbitals as well, but they compress the H–X–H angle compared to pure bonding orbitals.
2. Hypervalent Molecules (more than 8 e⁻) are often best described with d‑orbital participation (sp³d, sp³d²).
3. Resonance: In delocalised systems (e.g., benzene), hybridization can be considered for the entire ring (sp² for all carbons).
4. Hybridization vs. Electron‑Pair Geometry: The VSEPR model gives the overall shape, while hybridization explains the type of orbitals involved.

3. Worked Example

Problem

Determine the hybridization of the central atom in the following molecules/ions:

1. NO₂
2. SO₄²⁻
3. PCl₅

Step‑by‑Step Solution

1. NO₂ (Nitrogen Dioxide)

• Lewis Structure:

      O
      |
  O = N
  

  (N has 5 valence e⁻, each O 6, total 13 e⁻ → a radical; one unpaired e⁻ on N).

• Count of electron domains (bonding + lone pairs) around N:

  • 2 N–O bonds (each counts as 1 domain)
  • 1 lone pair (from the unpaired electron) → 3 domains.

• Geometry: Trigonal planar (but distorted due to lone pair).

• Hybridization: sp² (3 hybrid orbitals).

• Bond angles: ≈ 120°, but actual O–N–O ≈ 134° due to lone pair repulsion.

2. SO₄²⁻ (Sulfate Ion)

• Lewis Structure: Sulfur double‑bonded to two oxygens and single‑bonded to two oxygens, each single‑bonded O carries a negative charge.

  • Sulfur has 6 valence e⁻; each O 6; overall 24 e⁻ → 24/2 = 12 bonds → 4 bonds to S.

• Electron domains around S: 4 σ bonds (each counts as one domain) → 4 domains.

• Geometry: Tetrahedral.

• Hybridization: sp³.

• Bond angles: 109.5° (ideal tetrahedral).

3. PCl₅ (Phosphorus Pentachloride)

• Lewis Structure: Phosphorus central, bonded to five Cl atoms.

  • Phosphorus has 5 valence e⁻; each Cl 7 → 5 bonds → 10 e⁻ → 10/2 = 5 domains.

• Electron domains around P: 5 σ bonds → 5 domains.

• Geometry: Trigonal bipyramidal.

• Hybridization: sp³d.

• Bond angles: 90° (axial–equatorial) and 120° (equatorial–equatorial).

4. Quick Revision Summary

• Hybridization = mixing of AOs on the same atom → new