How many electron domains are around the central atom? What is the electron-pair geometry of SO3? options: a) 3, trigonal pyramidal b) 4, bent c) 2, linear d) 3, trigonal planar e) 3, bent
The correct answer and explanation is:
The correct answer is d) 3, trigonal planar.
Sulfur trioxide (SO₃) is a molecule where the central sulfur atom is surrounded by three oxygen atoms. To determine the electron domains and electron-pair geometry, we need to analyze the bonding and structure of SO₃.
Step 1: Counting Electron Domains
An electron domain refers to a region where electrons are likely to be found around an atom, which includes bonding pairs (single, double, or triple bonds) and lone pairs of electrons. In SO₃, sulfur is the central atom, and it forms three double bonds with the three oxygen atoms. Each double bond counts as one electron domain. Since there are no lone pairs on the sulfur atom, the total number of electron domains around sulfur is 3.
Step 2: Electron-Pair Geometry
The geometry of a molecule depends on the arrangement of its electron domains, not just its atoms. With three electron domains around the sulfur atom, the electron-pair geometry follows the pattern of a trigonal planar arrangement. This geometry occurs when there are three electron domains that arrange themselves at 120° angles to minimize repulsion between them, according to the Valence Shell Electron Pair Repulsion (VSEPR) theory.
Step 3: Molecular Geometry
In the case of SO₃, the sulfur atom is bonded to three oxygen atoms with no lone pairs. Therefore, the molecular geometry also takes on the trigonal planar shape, with the oxygen atoms arranged symmetrically around the sulfur atom.
Conclusion
SO₃ has three electron domains around the sulfur atom, and the electron-pair geometry is trigonal planar. This corresponds to option d).