Draw the Lewis structure of PH3 molecule and state its electron domain geometry. The geometry of PH3 is pyramidal
The Correct Answer and Explanation is:
Lewis Structure of PH₃ (Phosphine)
Step-by-step Lewis Structure:
- Count total valence electrons:
- Phosphorus (P) is in group 15 and has 5 valence electrons
- Hydrogen (H) has 1 valence electron × 3 = 3 valence electrons
- Total = 5 + 3 = 8 valence electrons
- Determine central atom:
- Phosphorus is less electronegative than hydrogen, so it is the central atom.
- Connect atoms:
- Draw single bonds between phosphorus and each hydrogen atom (3 bonds)
- Each bond uses 2 electrons, so 3 bonds = 6 electrons used
- Place remaining electrons:
- 8 total electrons − 6 used in bonds = 2 electrons left
- Place the remaining 2 electrons as a lone pair on phosphorus
Lewis Structure of PH₃:
lessCopyEdit H
|
H — P — H
:
- The colon (:) represents the lone pair on phosphorus.
- Each hydrogen has a single bond and a full valence shell (2 electrons).
- Phosphorus has three single bonds and one lone pair, making a total of 8 electrons (stable octet).
Electron Domain Geometry and Molecular Shape:
- Electron domain geometry refers to the spatial arrangement of all electron domains (bonding and lone pairs) around the central atom.
- Phosphorus in PH₃ has four electron domains: three bonding pairs and one lone pair.
Electron Domain Geometry: Tetrahedral
Molecular Geometry (Shape): Trigonal Pyramidal
The lone pair on phosphorus repels the bonding pairs, pushing the hydrogen atoms downward, creating a pyramidal shape rather than a flat, trigonal planar shape.
Explanation:
PH₃ is similar to ammonia (NH₃) in terms of electron arrangement. The presence of the lone pair on phosphorus causes the molecule to adopt a trigonal pyramidal shape even though the electron domain geometry is tetrahedral. The lone pair occupies more space than bonding pairs and pushes the hydrogen atoms closer together, making the molecule non-linear and giving it its characteristic three-dimensional pyramidal geometry. This also contributes to the slight polarity of the molecule.
