From your models of SF4 , BrF3, and XeF4 deduce whether different atom arrangements, called geometrical isomers are possible; if so, sketch them below. Indicate the preferred geometry for each case and suggest a reason for your choice. Indicate which structures have dipole moments and show their direction.
(A) SF4
(B) BrF3
(C) XeF4
The correct answer and explanation is :
(A) SF4 (Sulfur Tetrafluoride)
- Geometry: The molecule has a see-saw shape, which is derived from a trigonal bipyramidal electron geometry, with one of the equatorial positions occupied by a lone pair.
- Isomer Possibility: There are no significant geometrical isomers for SF4 because the lone pair occupies one of the equatorial positions, leading to a unique see-saw shape.
- Dipole Moment: SF4 has a net dipole moment because the molecule is asymmetrical. The electronegativity of fluorine pulls electrons away from sulfur, and the shape causes these dipoles to not cancel out.
- Direction of Dipole Moment: The dipole moment points toward the fluorine atoms and away from the sulfur atom.
(B) BrF3 (Bromine Trifluoride)
- Geometry: BrF3 adopts a T-shaped geometry, similar to the structure of SF4 but with two lone pairs in the axial positions, resulting in a more compact shape.
- Isomer Possibility: Geometrical isomerism is not possible for BrF3, as the lone pairs on the axial positions restrict any alternate spatial arrangements.
- Dipole Moment: BrF3 has a net dipole moment because of the T-shaped structure, which is polar.
- Direction of Dipole Moment: The dipole points towards the fluorine atoms, away from the central bromine atom.
(C) XeF4 (Xenon Tetrafluoride)
- Geometry: XeF4 adopts a square planar geometry, which is typical for molecules with 4 bonding pairs and 2 lone pairs in an octahedral electron geometry.
- Isomer Possibility: There are no geometrical isomers for XeF4. The presence of two lone pairs on opposite sides of the xenon atom ensures symmetry, resulting in a single, well-defined geometry.
- Dipole Moment: XeF4 has no net dipole moment. The square planar geometry is symmetric, and the individual bond dipoles cancel out.
- Direction of Dipole Moment: Since there is no net dipole moment, there is no direction.
Summary of Preferred Geometries and Dipole Moments:
- SF4: See-saw geometry with a dipole moment.
- BrF3: T-shaped geometry with a dipole moment.
- XeF4: Square planar geometry with no dipole moment.
Explanation:
- Electron Pair Geometry: The geometry of each molecule is influenced by the number of bonding pairs and lone pairs around the central atom, determined by the VSEPR (Valence Shell Electron Pair Repulsion) theory.
- Dipole Moment: A dipole moment arises in molecules with asymmetrical charge distributions. In SF4 and BrF3, the presence of lone pairs and the resulting asymmetry lead to a non-zero dipole moment, while XeF4’s symmetry cancels out individual dipoles.