Hybridisation is the mixing of atomic orbitals of comparable energies to form an equal number of hybrid orbitals. Different types of hybridisation involve different combinations of s, p and d orbitals.
1. sp³d Hybridisation
- Orbitals involved: 1 s + 3 p + 1 d
- d orbital used: d(z²)
- Number of hybrid orbitals: 5
- Geometry: Trigonal bipyramidal
- Example: PCl₅
2. sp³d² Hybridisation
- Orbitals involved: 1 s + 3 p + 2 d
- d orbitals used: d(z²) and d(x² − y²)
- Number of hybrid orbitals: 6
- Geometry: Octahedral
- Example: SF₆
3. dsp² Hybridisation
- Orbitals involved: 1 d + 1 s + 2 p
- d orbital used: d(x² − y²)
- Number of hybrid orbitals: 4
- Geometry: Square planar
- Example: [Ni(CN)₄]²⁻
4. d²sp³ Hybridisation
- Orbitals involved: 2 d + 1 s + 3 p
- d orbitals used: d(z²) and d(x² − y²), in the traditional textbook model
- Number of hybrid orbitals: 6
- Geometry: Octahedral
- Example: [Co(NH₃)₆]³⁺
5. d³sp³ Hybridisation
- Orbitals involved: 3 d + 1 s + 3 p
- d orbitals used: d(xy), d(yz) and d(xz), in the traditional textbook model
- Number of hybrid orbitals: 7
- Geometry: Pentagonal bipyramidal
- Example: [ZrF₇]³⁻
Summary Table
Important Note: The d-orbital assignments above follow the traditional textbook hybridisation model. Modern molecular orbital theory provides a more accurate description of bonding, especially for complexes involving transition metals.
| Hybridisation | d orbitals used | Number of hybrid orbitals | Geometry |
|---|---|---|---|
| sp³d | d(z²) | 5 | Trigonal bipyramidal |
| sp³d² | d(z²), d(x² − y²) | 6 | Octahedral |
| dsp² | d(x² − y²) | 4 | Square planar |
| d²sp³ | d(z²), d(x² − y²) | 6 | Octahedral |
| d³sp³ | d(xy), d(yz), d(xz) | 7 | Pentagonal bipyramidal |
Note: The d-orbital assignments follow the traditional textbook hybridisation model.
