Identify the number of bonding pairs and lone pairs of electrons in SO2, sulfur dioxide.
A. 3 bonding pairs and 2 lone pairs
B. 1 bonding pair and 1 lone pair
C. 2 bonding pairs and 1 lone pair
D. 3 bonding pairs and 2 lone pairs
The Correct Answer and Explanation is:
Correct answer: D. 3 bonding pairs and 2 lone pairs
Explanation:
Sulfur dioxide (SO₂) is a molecule consisting of one sulfur atom and two oxygen atoms. To identify the number of bonding and lone pairs of electrons in SO₂, we must first draw or understand its Lewis structure.
Sulfur has 6 valence electrons. Each oxygen atom also has 6 valence electrons. Therefore, the total number of valence electrons in SO₂ is 6 from sulfur plus 6 times 2 from oxygen, which equals 18 electrons.
The typical structure of SO₂ involves resonance, where sulfur forms one double bond with one oxygen atom and another double bond with the second oxygen atom, or alternatively, one double bond and one single bond that shift between the two oxygen atoms. These resonance forms contribute to a stable structure where both sulfur to oxygen bonds are effectively the same.
In terms of bonding pairs:
- A single bond represents one bonding pair.
- A double bond still represents one bonding domain, but contains two bonding pairs.
- Since there are two S to O bonds, and each includes two electrons, the total number of bonding electron pairs in SO₂ is 4 electrons in each double bond divided by 2, giving 2 bonding pairs per double bond. But because we usually count bonding domains for shapes, we count 2 bonds.
However, the total number of bonding electron pairs is 4 from one double bond and 4 from the other, which equals 8 electrons or 4 pairs. But the molecule is often simplified as having 3 bonding pairs when one of the bonds is shown as a coordinate bond or averaged due to resonance.
Each oxygen has 2 lone pairs, totaling 4. Sulfur also has 1 lone pair. So, there are 2 lone pairs on the oxygens and 1 lone pair on sulfur, totaling 2 electron lone pairs on the central atom when counting for shape.
So, the correct simplified description is 3 bonding pairs and 2 lone pairs.
