What is the electronic geometry and molecular geometry of the hypophosphite ion (PO2^3-)? Can you please provide an explanation also.
The correct answer and explanation is:
Correct Answer:
- Electronic Geometry: Tetrahedral
- Molecular Geometry: Trigonal pyramidal
Explanation (300 words):
The hypophosphite ion (PO₂³⁻) consists of a central phosphorus (P) atom bonded to two oxygen atoms, with a formal charge of –3 distributed over the ion.
Let’s go step-by-step to determine the electronic and molecular geometry:
Step 1: Count Valence Electrons
- Phosphorus (P) has 5 valence electrons.
- Each oxygen (O) has 6 valence electrons, for a total of 2 × 6 = 12.
- Add 3 electrons for the –3 charge.
- Total = 5 (P) + 12 (O) + 3 (charge) = 20 valence electrons
Step 2: Draw the Lewis Structure
- Place phosphorus in the center.
- Attach two oxygen atoms to phosphorus using single bonds (2 × 2 = 4 electrons).
- Complete octets of both oxygen atoms by adding lone pairs (2 × 6 = 12 electrons).
- This accounts for 16 electrons; 4 remain.
- These remaining electrons go as a lone pair on phosphorus.
- So, phosphorus has 3 regions: 2 bonding pairs (P–O bonds) and 1 lone pair.
Note: One oxygen is likely doubly bonded to reduce formal charges, making the bonding situation P=O and P–O⁻. Still, from a VSEPR (Valence Shell Electron Pair Repulsion) perspective, we count regions of electron density, not bond order.
Step 3: Determine Geometries
- There are 4 regions of electron density around P (2 bonds + 1 lone pair + 1 single bond).
- According to VSEPR theory:
- 4 regions → Tetrahedral electronic geometry
- With one lone pair → Trigonal pyramidal molecular geometry
Conclusion:
The electronic geometry of the PO₂³⁻ ion is tetrahedral, reflecting the 4 electron domains. However, because one domain is a lone pair, the actual molecular geometry becomes trigonal pyramidal, giving the ion its 3D shape.