Determine the electron geometry (eg), molecular geometry (mg), and polarity of SO3.
A) eg = trigonal pyramidal, mg = bent, nonpolar
B) eg = tetrahedral, mg = tetrahedral, nonpolar
C) eg = trigonal bipyramidal, mg = trigonal pyramidal, nonpolar
D) eg = tetrahedral, mg = trigonal pyramidal, polar
E) eg = trigonal planar, mg = trigonal planar, nonpolar
The Correct Answer and Explanation is :
To determine the electron geometry (eg), molecular geometry (mg), and polarity of sulfur trioxide (SO₃), we need to analyze its Lewis structure and molecular shape.
Lewis Structure of SO₃
- Valence Electrons Calculation:
- Sulfur (S) is in Group 16 and has 6 valence electrons.
- Each oxygen (O) is also in Group 16, contributing 6 valence electrons. Therefore, 3 oxygen atoms contribute a total of (3 \times 6 = 18) valence electrons.
- Total valence electrons = (6 + 18 = 24).
- Drawing the Structure:
- Sulfur is the central atom with three oxygen atoms bonded to it. Each oxygen atom forms a double bond with sulfur to fulfill the octet rule, leading to the structure: O=S=O and O on either side.
- All atoms have complete octets, and sulfur is able to expand its octet since it is in period 3 of the periodic table.
Electron and Molecular Geometry
- Electron Geometry: The presence of three double bonds around the central sulfur atom (with no lone pairs on sulfur) gives SO₃ a trigonal planar electron geometry. This is characterized by bond angles of approximately 120 degrees.
- Molecular Geometry: Since there are no lone pairs on the sulfur atom, the molecular geometry is also trigonal planar. Thus, both the electron geometry and molecular geometry for SO₃ are trigonal planar.
Polarity
- Polarity: To determine polarity, we examine the symmetry of the molecule. SO₃ is symmetrical with three identical S=O bonds arranged at 120-degree angles. The dipole moments from each bond cancel out due to this symmetry, making the overall molecule nonpolar.
Conclusion
Based on the analysis, the correct answer is:
E) eg = trigonal planar, mg = trigonal planar, nonpolar.
This conclusion is based on the molecular structure of SO₃, where the arrangement of bonds and absence of lone pairs lead to a nonpolar characteristic due to the symmetrical geometry.