Lewis structure of ClO3-

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Lewis structure of ClO3-
Lewis structure of ClO3 | Image: Root Memory

The Lewis structure of ClO3 contains two double bonds and one single bond, with chlorine in the center, and three oxygens on either side. The left oxygen atom and right oxygen atom have two lone pairs, the top oxygen atom has three lone pairs, and the chlorine atom has one lone pair.

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

Steps

By using the following steps, you can easily draw the Lewis structure of ClO3:

#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… chlorine is a group 17 element and oxygen is a group 16 element. Hence, chlorine has seven valence electrons and oxygen has six valence electrons.

Now ClO3 has one chlorine atom and three oxygen atoms.

So the total number of valence electrons = valence electrons of chlorine atom + (valence electrons of oxygen atom × 3)

And ClO3 has a negative (-1) charge, so we have to add one more electron.

Therefore, the total number of valence electrons = 7 + 18 + 1 = 26

  • 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 chlorine and oxygen as follows:

Electronegativity value of chlorine = 3.16
Electronegativity value of oxygen = 3.44

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

So now, put chlorine in the center and oxygens on either side. And draw the rough skeleton structure for the Lewis structure of ClO3 something like this:

Skeleton structure for Lewis structure of ClO3 | Image: Root Memory

#2 Show chemical bond

Place two electrons between the atoms to show a chemical bond. Since chlorine is surrounded by three oxygens, use six electrons to show three chemical bonds as follows:

Three chemical bonds shown between atoms | Image: Root Memory

#3 Mark lone pairs

As calculated earlier, we have a total of 26 valence electrons. And in the above structure, we have already used six valence electrons. Hence, twenty valence electrons are remaining.

Two valence electrons represent one lone pair. So twenty valence electrons = ten lone pairs.

Note that chlorine is 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 (chlorine) will get one lone pair.

So the Lewis structure of ClO3 looks something like this:

Lone pairs marked on Lewis structure of ClO3 | Image: Root Memory

In the above structure, you can see that the octet is completed on the central atom (chlorine), 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.

#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 chlorine atom

Valence electrons = 7
Nonbonding electrons = 2
Bonding electrons = 6

Formal charge = 7 – 2 – ½ (6) = +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 ClO3 looks something like this:

Formal charges are not closer to zero | Image: Root Memory

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.

#5 Convert lone pair and calculate formal charge again

As mentioned earlier, chlorine 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 chlorine atom. And then, the Lewis structure of ClO3 looks something like this:

Lone pair of left and right oxygen is converted, and octet is completed on atoms | Image: Root Memory

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 chlorine atom

Valence electrons = 7
Nonbonding electrons = 2
Bonding electrons = 10

Formal charge = 7 – 2 – ½ (10) = 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 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 ClO3 looks something like this:

Formal charges are calculated, and got the most stable Lewis structure of ClO3 | Image: Root Memory

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 ClO3.

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

Now ClO3 is an ion having a negative (-1) charge, so draw brackets around the above Lewis structure and mention that charge on the top right corner. And then, the Lewis structure of ClO3 looks something like this:

Lewis structure of ClO3 showing a negative (-1) charge | Image: Root Memory

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Deep

Rootmemory.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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