SO2 Lewis structure

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SO2 Lewis structure
SO2 Lewis structure | Image: Learnool

The SO2 Lewis structure depicts the molecular arrangement of sulfur dioxide, which consists of one sulfur atom and two oxygen atoms. In the SO2 Lewis structure, there is a double bond between the sulfur atom and each oxygen atom. Furthermore, each oxygen atom possesses two lone pairs, and the sulfur atom has one lone pair.

To draw the SO2 Lewis structure correctly, begin by sketching the molecule and marking the lone pairs on the atoms. Next, calculate and mark the formal charges on the atoms and make necessary adjustments by converting lone pairs of the atoms. Repeat the process until all formal charges are minimized, and a stable Lewis structure is obtained. These steps ensure the correct distribution of electrons and the satisfaction of the octet rule for all atoms in the SO2 molecule.

Steps

Sketch the structure

Location of sulfur and oxygen on the periodic table | Image: Learnool

The first step in sketching the SO2 structure is to determine the total number of valence electrons. Since both sulfur and oxygen are in group 16 of the periodic table, they each have six valence electrons. As SO2 has one sulfur atom and two oxygen atoms, the total number of valence electrons can be calculated by adding up the valence electrons of each atom: 6 valence electrons for the sulfur atom and 12 valence electrons for the two oxygen atoms. Therefore, the total number of valence electrons in the SO2 molecule is 6 + 12 = 18.

The second step in sketching the SO2 structure is to determine the total number of electron pairs. To calculate this, divide the total number of valence electrons by 2. In the case of SO2, there are 18 valence electrons. Thus, the total electron pairs can be found by dividing 18 by 2, which gives a result of 9 electron pairs.

Once the total electron pairs have been identified, the next step is to determine the central atom for the SO2 molecule. The least electronegative atom is usually placed at the center, and in this case, sulfur has a lower electronegativity than oxygen. Therefore, assume that the central atom is sulfur and place it in the center, with one oxygen atom on either side. After determining the positions of the atoms, a rough sketch of the SO2 structure can be drawn.

Rough sketch of SO2 Lewis structure | Image: Learnool

Indicate lone pair

Once the rough sketch of the SO2 structure has been drawn, the next step is to identify and indicate the lone pairs on the atoms. It is important to note that there are a total of 9 electron pairs for the molecule, with two S – O bonds already shown in the sketch, utilizing four electron pairs. Therefore, the remaining seven electron pairs should be marked as lone pairs.

It’s worth noting that sulfur is a period 3 element, meaning it can accommodate more than 8 electrons in its valence shell. On the other hand, oxygen is a period 2 element, meaning it cannot hold more than 8 electrons in its valence shell.

To correctly indicate the lone pairs in the SO2 structure, it is important to start from the outside atoms, which in this case are the two oxygen atoms. Each oxygen atom will receive three lone pairs, while the central sulfur atom will have only one lone pair. These lone pairs can be marked on the rough sketch of the structure according to their respective atoms.

SO2 Lewis structure with lone pairs | Image: Learnool

Assign formal charge

To assign formal charges to the atoms in the SO2 molecule, use the formula: Formal charge = valence electrons – nonbonding electrons – ½ bonding electrons. The valence electrons for sulfur is 6, while it has 2 nonbonding electrons and 4 bonding electrons. Plugging these values into the formula gives a formal charge of +2 for the sulfur atom. For each oxygen atom, the valence electrons is 6, there are 6 nonbonding electrons and 2 bonding electrons, leading to a formal charge of -1.

Atom
Valence electron
Nonbonding electron
Bonding electron
Formal charge
Sulfur 4 2 4 +2
Oxygen 6 6 2 -1

As both the sulfur and oxygen atoms have charges, they should be marked on the sketch to clearly indicate their formal charges.

SO2 Lewis structure with formal charges | Image: Learnool

The current Lewis structure is not stable as it has charges on both sulfur and oxygen atoms. In order to obtain a stable structure, it is necessary to reduce the formal charges by converting lone pairs to bonds.

Minimize formal charge

To reduce the formal charges on the SO2 structure, one approach is to convert a lone pair of one of the oxygen atoms into a new bond with the sulfur atom. This will help to reduce the formal charges on the atoms and make the structure more stable.

Lone pair of left oxygen is converted, but still there are formal charges | Image: Learnool

To further minimize the formal charges on the SO2 structure, it is necessary to convert another lone pair of the oxygen atom into a new bond with the sulfur atom. This will help to reduce the charges on the atoms and increase the stability of the structure.

Lone pair of right oxygen is converted, and got the stable Lewis structure of SO2 | Image: Learnool

The Lewis structure for SO2 satisfies the octet rule as the central sulfur atom and the two surrounding oxygen atoms each have eight electrons in their valence shell. This arrangement results in a more stable structure compared to previous attempts. Therefore, this final structure represents the stable Lewis structure of SO2.

Next: NO2 Lewis structure

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Deep

Learnool.com was founded by Deep Rana, who is a mechanical engineer by profession and a blogger by passion. He has a good conceptual knowledge on different educational topics and he provides the same on this website. He loves to learn something new everyday and believes that the best utilization of free time is developing a new skill.

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