To draw the Lewis structure for sulfur trioxide (SO3), we first need to count the total number of valence electrons. Sulfur has 6 valence electrons, and each oxygen atom has 6 valence electrons. Therefore, for SO3, the total is:
6 (S) + 3 × 6 (O) = 24 valence electrons.
Next, we position the sulfur atom in the center since it is less electronegative, and place the three oxygen atoms around it. To satisfy the octet rule, we can draw double bonds between the sulfur and each oxygen atom (S=O). After forming these double bonds, each oxygen atom will have two lone pairs of electrons left. The structure will look like this:
The resulting Lewis structure has no lone pairs on the sulfur atom but has double bonds with each oxygen.
Now, let’s determine the electron groups and the geometry:
- Number of electron groups: There are three double bonds, so there are 3 electron groups around the sulfur atom.
- Electron geometry: Based on the VSEPR theory, having three electron groups results in a trigonal planar geometry.
- Molecular shape: With the same arrangement and no lone pairs on the central atom, the molecular shape is also trigonal planar.
Finally, we consider the polarity of the molecule. The symmetrical arrangement of the three oxygen atoms around the sulfur means that the dipole moments from each S=O bond cancel each other out. Thus, SO3 is nonpolar.
In summary, the Lewis structure of SO3 shows that it has 3 electron groups, a trigonal planar electron geometry, a molecular shape that is also trigonal planar, and it is a nonpolar molecule.