A prominent example of sp3d hybridization is the phosphorus pentachloride (PCl5) molecule.
Understanding sp3d Hybridization
Hybridization is the concept of mixing atomic orbitals to form new hybrid orbitals suitable for the pairing of electrons to form chemical bonds. sp3d hybridization involves the mixing of one s orbital, three p orbitals, and one d orbital from the valence shell of the central atom. This type of hybridization is typically observed in elements from the third period or beyond, as they possess vacant d orbitals that can participate in bonding, allowing for the expansion of their octet.
Molecular Geometry of sp3d Hybridization
The formation of five equivalent sp3d hybrid orbitals leads to a specific molecular geometry. The only conceivable molecule geometry for sp3d hybridised centre atoms is trigonal bipyramidal. Trigonal bipyramidal shape is likewise the result if all five hybrid orbitals form bonds. This geometry is characterized by:
- Three equatorial positions: These lie in a plane, forming a trigonal planar arrangement around the central atom with bond angles of 120°.
- Two axial positions: These are perpendicular to the equatorial plane, with bond angles of 90° to the equatorial bonds.
Key Examples of sp3d Hybridization
Let's explore PCl5 and other common molecules that exhibit sp3d hybridization:
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Phosphorus Pentachloride (PCl5)
- In PCl5, the central phosphorus (P) atom is sp3d hybridized. Phosphorus has five valence electrons, and it forms five sigma bonds with five chlorine (Cl) atoms.
- The molecule adopts a trigonal bipyramidal geometry, as predicted by VSEPR theory and confirmed by experimental observations.
- Three Cl atoms occupy the equatorial positions, and two Cl atoms occupy the axial positions. The axial bonds are typically slightly longer than the equatorial bonds due to greater repulsion from the equatorial bond pairs.
- Learn more about PCl5 structure and bonding on educational platforms like LibreTexts Chemistry or Khan Academy.
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Sulfur Tetrafluoride (SF4)
- The central sulfur (S) atom in SF4 is sp3d hybridized. Sulfur forms four sigma bonds with fluorine (F) atoms and has one lone pair of electrons.
- The presence of the lone pair distorts the trigonal bipyramidal geometry, resulting in a seesaw molecular shape.
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Xenon Difluoride (XeF2)
- Xenon (Xe) in XeF2 is sp3d hybridized. It forms two sigma bonds with fluorine atoms and has three lone pairs.
- The lone pairs occupy the equatorial positions to minimize repulsion, leading to a linear molecular geometry.
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Triiodide Ion (I3-)
- The central iodine (I) atom in the triiodide ion (I3-) is sp3d hybridized. It forms two sigma bonds with the other two iodine atoms and has three lone pairs.
- Similar to XeF2, the three lone pairs reside in the equatorial plane, giving the ion a linear molecular geometry.
Distinguishing Hybridization Types
When examining the principles of molecular bonding and geometry, it is important to note that different hybridization states lead to distinct molecular shapes. For instance, the creation of the methane molecule, a classic example in chemistry, involves sp3 hybridization, resulting in a tetrahedral geometry, which is fundamentally different from the trigonal bipyramidal shape associated with sp3d hybridization. The table below highlights key differences between common hybridization types:
| Hybridization Type | Number of Hybrid Orbitals | Molecular Geometry (if no lone pairs) | Example |
|---|---|---|---|
| sp | 2 | Linear | Carbon dioxide (CO2), Acetylene (C2H2) |
| sp2 | 3 | Trigonal Planar | Boron trifluoride (BF3), Ethene (C2H4) |
| sp3 | 4 | Tetrahedral | Methane (CH4), Ammonia (NH3), Water (H2O) |
| sp3d | 5 | Trigonal Bipyramidal | Phosphorus pentachloride (PCl5), Sulfur tetrafluoride (SF4) |
| sp3d2 | 6 | Octahedral | Sulfur hexafluoride (SF6), Iodine heptafluoride (IF7) |
