Give the point group for the molecule BrF3.
The correct answer and explanation is:
Correct Answer: C2v
Bromine trifluoride (BrF₃) belongs to the C₂v point group. This classification is based on its molecular geometry and the types of symmetry elements it possesses.
BrF₃ has a T-shaped molecular geometry. It consists of a central bromine atom bonded to three fluorine atoms. Bromine also has two lone pairs of electrons, which are located in the equatorial positions of a trigonal bipyramidal electron geometry. The three fluorine atoms occupy two axial and one equatorial position, resulting in the T-shape.
To assign the point group, analyze the symmetry elements:
- C₂ axis (principal axis): The molecule has a two-fold rotational axis passing through the central Br atom and the middle fluorine atom (the one in the equatorial plane) and perpendicular to the plane of the other two fluorine atoms. A 180-degree rotation swaps the two axial fluorine atoms.
- σv planes (vertical mirror planes): There are two mirror planes:
- One contains the central atom and all three fluorine atoms (the molecular plane).
- The second is perpendicular to this plane and bisects the angle between the two axial fluorine atoms.
These elements (C₂ and two σv planes) define the C₂v point group.
The C₂v point group is one of the common groups for molecules with T-shaped geometry. This point group is important in molecular spectroscopy and group theory because it helps predict vibrational modes, infrared activity, and electronic transitions.
In conclusion, BrF₃ has a T-shaped molecular structure with a C₂ axis and two mirror planes, placing it in the C₂v point group. Identifying the correct point group helps in understanding the physical and chemical behavior of the molecule, including its polarity and spectroscopic characteristics.