Lewis structure of SO42-

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The Lewis structure of SO₄^2- contains two single bonds and two double bonds, with sulfur in the center, and four oxygens on either side. The top oxygen atom and bottom oxygen atom has three lone pairs, the left oxygen atom and right oxygen atom has two lone pairs, and the sulfur atom does not have any lone pair.

Plus, there is a negative (-1) charge on the top oxygen atom and bottom oxygen atom.

Steps

By using the following steps, you can easily draw the Lewis structure of SO₄^2-.

#1 Draw skeleton
#2 Show chemical bond
#3 Mark lone pairs
#4 Calculate formal charge and check stability (if octet is already completed on central atom)
#5 Convert lone pair and calculate formal charge again (if formal charges are not closer to zero)

Let’s one by one discuss each step in detail.

#1 Draw skeleton

In this step, first calculate the total number of valence electrons. And then, decide the central atom.

• Let’s calculate the total number of valence electrons

We know that… both sulfur and oxygen are the group 16 elements. Hence, both sulfur and oxygen have six valence electrons.

Now SO₄^2- has one sulfur atom and four oxygen atoms.

So the total number of valence electrons = valence electrons of sulfur atom + (valence electrons of oxygen atom × 4)

And SO₄^2- has a negative (-2) charge, so we have to add two more electrons.

Therefore, the total number of valence electrons = 6 + 24 + 2 = 32

• Now decide the central atom

The atom with the least electronegative value is placed at the center. By looking at the periodic table, we get the electronegativity values for sulfur and oxygen as follows:

Electronegativity value of sulfur = 2.58
Electronegativity value of oxygen = 3.44

Obviously, sulfur is less electronegative than oxygen. Hence, assume that sulfur is the central atom.

So now, put sulfur in the center and oxygens on either side. And draw the rough skeleton structure for the Lewis structure of SO₄^2- something like this:

Also read: How to draw Lewis structure of SiS₂ (5 steps)

#2 Show chemical bond

Place two electrons between the atoms to show a chemical bond. Since sulfur is surrounded by four oxygens, use eight electrons to show four chemical bonds as follows:

#3 Mark lone pairs

As calculated earlier, we have a total of 32 valence electrons. And in the above structure, we have already used eight valence electrons. Hence, twenty-four valence electrons are remaining.

Two valence electrons represent one lone pair. So twenty-four valence electrons = twelve lone pairs.

Note that sulfur is a period 3 element, so it can keep more than 8 electrons in its last shell. And oxygen is a period 2 element, so it can not keep more than 8 electrons in its last shell.

Also, make sure that you start marking these lone pairs on outside atoms first. And then, on the central atom.

The outside atoms are oxygens, so each oxygen will get three lone pairs. And the central atom (sulfur) will not get any lone pair, because all twelve lone pairs are used.

So the Lewis structure of SO₄^2- looks something like this:

In the above structure, you can see that the octet is completed on the central atom (sulfur), and also on the outside atoms. Therefore, the octet rule is satisfied.

Now calculate the formal charge and check the stability of the above structure.

Also read: How to draw Lewis structure of PBr₅ (4 steps)

#4 Calculate formal charge and check stability

The following formula is used to calculate the formal charges on atoms:

Formal charge = valence electrons – nonbonding electrons – ½ bonding electrons

Collect the data from the above structure and then, write it down below as follows:

• For sulfur atom

Valence electrons = 6
Nonbonding electrons = 0
Bonding electrons = 8

Formal charge = 6 – 0 – ½ (8) = +2

• For each oxygen atom

Valence electrons = 6
Nonbonding electrons = 6
Bonding electrons = 2

Formal charge = 6 – 6 – ½ (2) = -1

Mention the formal charges of atoms on the structure. So the Lewis structure of SO₄^2- looks something like this:

In the above structure, you can see that the formal charges of atoms are not closer to zero. Therefore, convert lone pair and calculate formal charge again.

Also read: How to draw Lewis structure of OCS (5 steps)

#5 Convert lone pair and calculate formal charge again

As mentioned earlier, sulfur is a period 3 element, so it can keep more than 8 electrons in its last shell.

So convert one lone pair from the two oxygen atoms to make a new bond with the sulfur atom. And then, the Lewis structure of SO₄^2- looks something like this:

Now one last thing we need to do is, calculate the formal charge again and check the stability of the above structure.

Formal charge = valence electrons – nonbonding electrons – ½ bonding electrons

Collect the data from the above structure and then, write it down below as follows:

• For sulfur atom

Valence electrons = 6
Nonbonding electrons = 0
Bonding electrons = 12

Formal charge = 6 – 0 – ½ (12) = 0

• For left oxygen and right oxygen atom

Valence electrons = 6
Nonbonding electrons = 4
Bonding electrons = 4

Formal charge = 6 – 4 – ½ (4) = 0

• For top oxygen and bottom oxygen atom

Valence electrons = 6
Nonbonding electrons = 6
Bonding electrons = 2

Formal charge = 6 – 6 – ½ (2) = -1

Mention the formal charges of atoms on the structure. So the Lewis structure of SO₄^2- looks something like this:

In the above structure, you can see that the formal charges of atoms are closer to zero. Therefore, this is the most stable Lewis structure of SO₄^2-.

And each horizontal line drawn in the above structure represents a pair of bonding valence electrons.

Now SO₄^2- is an ion having a negative (-2) charge, so draw brackets around the above Lewis structure and mention that charge on the top right corner. And then, the Lewis structure of SO₄^2- looks something like this:

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Related

• Lewis structure of SiS₂
• Lewis structure of PBr₅
• Lewis structure of OCS
• Lewis structure of H₃O⁺
• Lewis structure of AsH₃

External links

• Lewis Structure for SO42- (Sulfate Ion) – The University of Maryland
• SO42- Lewis Structure (Sulfate ion) – Chemistry School
• SO42- lewis structure, molecular geometry, and hybridization – Topblogtenz
• SO42- Lewis Structure in 5 Steps (With Images) – Pediabay
• SO42 Lewis Structure, Molecular Geometry, Hybridization, and Polarity – Techiescientist
• Lewis Structure of SO4(2-) (Sulfate) CORRECT – Pinterest
• SO42- Lewis Structure – The Geoexchange
• What is the Lewis structure for SO42-? – Homework.Study.com
• SO42- Lewis Structure, Hybridization, Bond Angle and Molecular Geometry – Geometry of Molecules
• Lewis Dot of Sulfate SO42- – Kent’s Chemistry
• For SO42-, sulfate ion, draw the Lewis structure (by counting valence electrons of each atom) – Course Hero
• Why can’t SO4 2- Lewis structure have 3 double bonds instead of 2 as the formal charge would be -1 on sulfur and -1 on oxygen instead of -1 on one oxygen and -1 on another oxygen with 2 double bonds? – Reddit
• In the sulphate ion, SO42-, the sulphur atom is the central atom with the other 4 oxygen atoms attached to it – Pearson
• What is the procedure to draw the Lewis dot structure of sulfate ion? – Quora
• For SO42 -, sulfate ion, draw the Lewis structure (by counting valence electrons of each atom) – Chegg
• Draw lewis structure for SO42-. Whether they obey the octet rule and if any coordinate covalent forms forms and its shape – Bartleby
• SO42- Geometry and Hybridization – Chemistry Steps