# SO42- Lewis structure

The SO42- Lewis structure depicts the molecular arrangement of sulfate, which consists of one sulfur atom and four oxygen atoms. The structure has two double bonds and two single bonds arranged around the sulfur atom, with each of the four oxygen atoms attached to it. Within this arrangement, the oxygen atoms that form double bonds have two lone pairs, while the oxygen atoms that form single bonds have three lone pairs. Both oxygen atoms that are bonded to sulfur with a single bond carry a negative (-1) charge.

To accurately draw this Lewis structure, it’s important to follow a series of steps. Begin by sketching a rough outline of the molecular arrangement. Next, identify any lone pairs on the atoms within the structure. If there are formal charges present, indicate them on the appropriate atoms. To minimize these charges, convert any lone pairs of electrons as needed and repeat this process until all charges are minimized. Ensure that the octet rule is fulfilled for both the central atom and the surrounding atoms. By following these steps, the SO42- Lewis structure can be accurately drawn.

Contents

## Steps

### Sketch the structure

The initial step in drawing the SO42- Lewis structure is to calculate the total number of valence electrons present in the molecule. Since sulfur and oxygen belong to group 16 of the periodic table, they each have six valence electrons. As SO42- contains one sulfur atom and four oxygen atoms, the total number of valence electrons can be calculated by adding up the valence electrons of each atom. A sulfur atom has six valence electrons, while four oxygen atoms have a total of 24 valence electrons, resulting in a sum of 30 valence electrons. Since SO42- carries a negative (-2) charge, two more electrons must be added to the count, resulting in a total of 32 valence electrons for SO42-.

The second step in sketching the SO42- Lewis structure involves determining the total number of electron pairs. With 32 valence electrons present in SO42-, the total number of electron pairs can be found by dividing this value by two. This results in a total of 16 electron pairs.

The third step in sketching the SO42- Lewis structure is to determine the central atom. The atom with the lowest electronegativity is usually placed at the center. In the case of SO42-, sulfur has a lower electronegativity than oxygen. Therefore, sulfur is placed at the center, and the oxygen atoms are arranged around it. Once the central atom is determined, it’s time to draw a rough sketch of the molecular structure.

### Indicate lone pair

With the rough sketch of the SO42- molecule complete, the next step is to indicate the presence of any lone pairs on the atoms. There are a total of 16 electron pairs in the structure, with four S – O bonds already depicted. These four S – O bonds utilize eight electron pairs. As a result, the remaining 12 electron pairs are lone pairs that need to be marked on the sketch.

It’s important to keep in mind that sulfur is a period 3 element, which means it can hold more than eight electrons in its outer shell. In contrast, oxygen is a period 2 element and can only hold up to eight electrons in its outer shell.

To accurately indicate the lone pairs in the SO42- Lewis structure, it’s important to start with the outer atoms first. In this case, the four oxygen atoms are the outer atoms. Therefore, each oxygen atom will receive three lone pairs of electrons. Since all 12 electron pairs are already accounted for, there are no remaining lone pairs to be indicated on the central sulfur atom.

### Assign formal charge

To assign formal charges in the SO42- Lewis structure, use the following formula: Formal charge = valence electrons – nonbonding electrons – ½ bonding electrons. For the sulfur atom, the formal charge can be calculated as 6 – 0 – ½(8) = +2. Meanwhile, for each oxygen atom, the formal charge can be calculated as 6 – 6 – ½(2) = -1.

 Atom Valence electron Nonbonding electron Bonding electron Formal charge Sulfur 6 0 8 +2 Oxygen 6 6 2 -1

Since both sulfur and oxygen atoms have formal charges, it’s important to indicate them on the structure.

The current SO42- Lewis structure is unstable because it contains formal charges on the atoms. To create a stable structure, it’s necessary to minimize these charges. This can be achieved by converting lone pairs of electrons into bonding pairs.

### Minimize formal charge

To stabilize the Lewis structure, a lone pair of the oxygen atom should be converted into a new S – O bond with the sulfur atom. This conversion will reduce the formal charge on the oxygen atom from -1 to 0 and the formal charge on the sulfur atom from +2 to +1. The result will be a more stable SO42- Lewis structure.

To further reduce the charges on the sulfur and oxygen atoms, convert another lone pair of the oxygen atom to make a new S – O bond with the sulfur atom.

The Lewis structure of SO42- is now complete, with the central atom sulfur and the four oxygen atoms on either side forming an octet, satisfying the octet rule. However, the two oxygen atoms still have a negative (-1) charge. This is acceptable as the best Lewis structure is one where the most electronegative atom has a negative charge. Since oxygen is the most electronegative element in this molecule, having a negative charge on the oxygen atoms is preferred. This structure is also more stable than the previous ones. Thus, it is the most stable Lewis structure for SO42-. Finally, to indicate the overall charge on the ion, draw brackets around the structure and place the charge (-2) outside the brackets.

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