Draw BFCl 2 (assume the molecule is planar) and with suitable diagrams show ALL the symmetry elements possessed by this molecule. Identify the point group of this molecule. 2. If BFCl 2 is non-planar instead of planar, identify all of the symmetry elements possessed by this molecule and identify its point group.
The Correct Answer and Explanation is :
To address this, I will explain the symmetry elements, point group identification, and the implications of BFCl₂ being planar or non-planar. Here’s the detailed analysis:
1. BFCl₂ (Planar):
Structure:
BFCl₂ is planar, with boron at the center and three substituents (F, Cl, Cl) forming a trigonal planar geometry.
Symmetry Elements:
- E (Identity): Every molecule has this symmetry element.
- C₃ (Principal Axis of Rotation): A 120° rotation around the axis passing through boron and perpendicular to the plane leaves the molecule unchanged.
- σ_v (Vertical Planes): Three vertical planes pass through B and each B–X bond (F or Cl). These planes include the principal axis.
- σ_h (Horizontal Plane): The plane of the molecule itself is a horizontal plane of symmetry.
- S₃ (Improper Axis): A 120° rotation around the C₃ axis, followed by a reflection in σ_h, also leaves the molecule unchanged.
Point Group:
The planar BFCl₂ belongs to the D3hD_{3h} point group due to the presence of C₃, σ_v, σ_h, and S₃.
2. BFCl₂ (Non-Planar):
Structure:
If BFCl₂ is non-planar, boron is at the center with the substituents (F, Cl, Cl) arranged in a trigonal pyramidal geometry, breaking the planar symmetry.
Symmetry Elements:
- E (Identity): Present as always.
- C₃ (Principal Axis of Rotation): A 120° rotation around the axis passing through boron and perpendicular to the base remains valid.
- σ_v (Vertical Planes): Only one vertical plane exists due to the asymmetry introduced by non-planarity.
Point Group:
The non-planar BFCl₂ belongs to the C3vC_{3v} point group, characterized by a C₃ axis and three σ_v planes.
Conclusion:
- Planar BFCl₂ has more symmetry, belonging to D3hD_{3h}.
- Non-planar BFCl₂ has reduced symmetry, belonging to C3vC_{3v}.
This change in geometry significantly reduces the number of symmetry elements, which alters the point group classification.