Determine the geometry of the BrCl3 molecule using the VSEPR theory. Of molecule Write the symmetry elements and find the point group. (Br: VIIA, Cl: VIIA)
The correct answer and explanation is:
Correct Answer:
- Molecular Geometry (VSEPR Theory): T-shaped
- Symmetry Elements: Identity (E), one C₂ axis, two vertical mirror planes (σᵥ)
- Point Group: C₂v
Explanation:
To determine the geometry of the BrCl₃ molecule using the Valence Shell Electron Pair Repulsion (VSEPR) theory, start by analyzing the number of valence electrons and electron domains around the central atom.
Bromine (Br), being in Group VIIA, has 7 valence electrons. In BrCl₃, bromine forms three single bonds with three chlorine atoms. This uses 3 of its 7 valence electrons, leaving 4 electrons (2 lone pairs) on the bromine atom. Therefore, there are 5 regions of electron density (3 bonding pairs and 2 lone pairs) around the bromine atom.
According to VSEPR theory, 5 regions of electron density adopt a trigonal bipyramidal electron geometry. In this arrangement, the lone pairs prefer equatorial positions to minimize electron pair repulsion. This leaves the three chlorine atoms occupying two axial and one equatorial positions, which results in a T-shaped molecular geometry.
Now for symmetry:
- The identity element (E) is always present.
- There is a C₂ (twofold) rotation axis through the central atom and perpendicular to the linear part of the T-shape.
- There are two vertical mirror planes (σᵥ): one contains the central atom and the linear Cl–Br–Cl axis, and another is perpendicular to it, bisecting the angle between the other Cl atom and the linear axis.
These symmetry elements correspond to the C₂v point group. This point group includes one C₂ axis and two σᵥ planes. BrCl₃ does not have an inversion center or horizontal mirror plane, confirming its classification.
Thus, BrCl₃ is a T-shaped molecule with C₂v symmetry and belongs to the C₂v point group.