How many electron domains (atoms and lone pairs) surround the central sulfur? b. What is the EDG of this molecule (look at atoms and lone pairs)? Draw this VSEPR structure using wedges and dashes next to the Lewis structure above. c. What is the molecular geometry of this molecule (look only at the atoms)? d. What is the approximate O-S-O bond angle? e. Place the partial positive and negative charges on the S and O atoms, based on their relative electronegativities. Is SO2 a polar compound? (yes/no)
The Correct Answer and Explanation is:
a. How many electron domains (atoms and lone pairs) surround the central sulfur?
There are three electron domains around the central sulfur atom. These include two bonding domains from the two oxygen atoms and one lone pair of electrons on the sulfur.
b. What is the electron domain geometry (EDG) of this molecule?
The electron domain geometry of SO₂ is trigonal planar, because there are three regions of electron density (two bonds and one lone pair) around the central sulfur atom.
c. What is the molecular geometry of this molecule (based on atoms only)?
The molecular geometry of SO₂ is bent (or angular), due to the presence of a lone pair on the sulfur that pushes the bonding pairs closer together.
d. What is the approximate O-S-O bond angle?
The O-S-O bond angle is approximately 120 degrees, but slightly less (around 119 degrees) due to the lone pair’s greater repulsion compared to bonding pairs.
e. Place the partial positive and negative charges on the S and O atoms. Is SO₂ a polar compound?
Oxygen is more electronegative than sulfur, so each oxygen atom pulls electron density toward itself. This gives each oxygen atom a partial negative charge (δ⁻) and the sulfur atom a partial positive charge (δ⁺).
Since the molecule is bent and the dipoles do not cancel out, SO₂ is a polar molecule.
Summary Explanation
Sulfur dioxide (SO₂) is a molecule consisting of one sulfur atom bonded to two oxygen atoms. To understand its shape and polarity, we apply Valence Shell Electron Pair Repulsion (VSEPR) theory. The central sulfur atom has six valence electrons. Each sulfur-oxygen double bond uses two electrons from sulfur. That accounts for four electrons. The remaining two electrons form a lone pair on sulfur.
This gives us a total of three electron domains around sulfur—two bonding domains (from the two oxygen atoms) and one nonbonding domain (lone pair). According to VSEPR theory, three electron domains adopt a trigonal planar electron domain geometry to minimize repulsion.
However, since only two of the domains are bonds to atoms, the actual molecular geometry is bent or angular. The lone pair on sulfur repels the bonding pairs slightly more strongly, compressing the bond angle slightly below 120 degrees, typically around 119 degrees.
Electronegativity differences also play a role in the molecule’s behavior. Oxygen is significantly more electronegative than sulfur, so each oxygen attracts bonding electrons more strongly. This creates a dipole with oxygen having a partial negative charge and sulfur a partial positive charge. The molecule’s bent shape ensures these dipoles do not cancel out.
As a result, SO₂ is a polar compound. Its molecular polarity gives it interesting chemical and physical properties, such as its role as an acid anhydride and its solubility in water. The polar nature also contributes to its ability to act as a greenhouse gas and participate in atmospheric chemical reactions.
