IF₅ has square pyramidal geometry, while PF₅ has trigonal bipyramidal geometry.
IF₅ (Iodine Pentafluoride):
- Central atom: Iodine (I)
- Bonding pairs: 5 (with F atoms)
- Lone pairs: 1
- Total electron pairs: 6
- Geometry: Square pyramidal
- Electron geometry: Octahedral
- Lone pair occupies one position, creating square pyramid
PF₅ (Phosphorus Pentafluoride):
- Central atom: Phosphorus (P)
- Bonding pairs: 5 (with F atoms)
- Lone pairs: 0
- Total electron pairs: 5
- Geometry: Trigonal bipyramidal
- Two axial positions (180° apart)
- Three equatorial positions (120° apart)
Why the Difference? The presence of a lone pair on iodine distorts the geometry from trigonal bipyramidal to square pyramidal.
Key Takeaways:
- IF₅: square pyramidal (6 electron pairs total)
- PF₅: trigonal bipyramidal (5 electron pairs total)
- Lone pairs influence molecular shape
- VSEPR theory explains geometries