Lewis structure of H2CO3

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The Lewis structure of H₂CO₃ contains one double bond and four single bonds, with carbon in the center, and two hydrogens and three oxygens on either side. There are two lone pairs on each oxygen atom, and carbon atom and hydrogen atom do not have any lone pair.

Steps

By using the following steps, you can easily draw the Lewis structure of H₂CO₃.

#1 Draw skeleton
#2 Show chemical bond
#3 Mark lone pairs
#4 Complete octet on central atom
#5 Calculate formal charge and check stability

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… hydrogen is a group 1 element, carbon is a group 14 element, and oxygen is a group 16 element. Hence, hydrogen has one valence electron, carbon has four valence electrons, and oxygen has six valence electrons.

Now H₂CO₃ has two hydrogen atoms, one carbon atom, and three oxygen atoms.

So the total number of valence electrons = (valence electrons of hydrogen atom × 2) + valence electrons of carbon atom + (valence electrons of oxygen atom × 3)

Therefore, the total number of valence electrons = 2 + 4 + 18 = 24

• Now decide the central atom

We can not assume hydrogen as the central atom, because the central atom is bonded with at least two other atoms. And hydrogen has only one electron in its last shell, so it can not make more than one bond.

Therefore, choose the central atom from carbon and oxygen.

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

Electronegativity value of carbon = 2.55
Electronegativity value of oxygen = 3.44

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

So now, put carbon in the center and hydrogens and oxygens on either side. And draw the rough skeleton structure for the Lewis structure of H₂CO₃ something like this:

Also read: How to draw Lewis structure of CH₃OCH₃ (4 steps)

#2 Show chemical bond

Place two electrons between the atoms to show a chemical bond. Since carbon is surrounded by two hydrogens and three oxygens, use ten electrons to show five chemical bonds as follows:

#3 Mark lone pairs

As calculated earlier, we have a total of 24 valence electrons. And in the above structure, we have already used ten valence electrons. Hence, fourteen valence electrons are remaining.

Two valence electrons represent one lone pair. So fourteen valence electrons = seven lone pairs.

Note that hydrogen is a period 1 element, so it can not keep more than 2 electrons in its last shell. And both (carbon and oxygen) are the period 2 elements, so they can not keep more than 8 electrons in their 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 hydrogens and oxygens. But hydrogen can not keep more than 2 electrons in its last shell. Hence, don’t mark the lone pairs on hydrogen.

So bottom oxygen will get three lone pairs, and top oxygen and right oxygen will get two lone pairs. And the central atom (carbon) will not get any lone pair, because all seven lone pairs are used.

Now draw the Lewis structure of H₂CO₃ something like this:

In the above structure, you can see that the octet is completed on outside atoms. But, the central atom (carbon) doesn’t form an octet.

So in the next step, we have to complete the octet on the central atom.

Also read: How to draw Lewis structure of PBr₃ (4 steps)

#4 Complete octet on central atom

Remember that carbon is a period 2 element, so it can not keep more than 8 electrons in its last shell.

Now carbon already has six valence electrons. Hence, carbon needs two more valence electrons to complete its octet.

So convert one lone pair from the bottom oxygen atom to make a new bond with the carbon atom. And then, the Lewis structure of H₂CO₃ looks something like this:

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

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

Also read: How to draw Lewis structure of CH₃Br (4 steps)

#5 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 each hydrogen atom

Valence electrons = 1
Nonbonding electrons = 0
Bonding electrons = 2

Formal charge = 1 – 0 – ½ (2) = 0

• For carbon atom

Valence electrons = 4
Nonbonding electrons = 0
Bonding electrons = 8

Formal charge = 4 – 0 – ½ (8) = 0

• For each oxygen atom

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

Formal charge = 6 – 4 – ½ (4) = 0

Mention the formal charges of atoms on the structure. So the Lewis structure of H₂CO₃ looks something like this:

In the above structure, you can see that the formal charges of all atoms are zero. Therefore, this is the stable Lewis structure of H₂CO₃.

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

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Related

• Lewis structure of CH₃OCH₃
• Lewis structure of PBr₃
• Lewis structure of CH₃Br
• Lewis structure of XeO₃
• Lewis structure of C₃H₆

External video

• H2CO3 Lewis Structure: How to Draw the Lewis Structure for Carbonic Acid – YouTube • Wayne Breslyn

External links

• H2CO3 (Carbonic Acid) Lewis Structure – Chemistry School
• H2CO3 Lewis structure, molecular geometry, hybridization, polarity – Topblogtenz
• H2CO3 Lewis Structure in 6 Steps (With Images) – Pediabay
• Chemical Bonding: H2CO3 Lewis Structure – The Geoexchange
• What is the Lewis dot structure for H2CO3? – Quora
• H2CO3 Lewis Structure, Molecular Geometry, Hybridization, Polar or Nonpolar – Studocu
• Draw and explain the Lewis structure for H2CO3 – Homework.Study.com
• Which is a correct Lewis structure for carbonic acid, H2CO3? – Chegg
• H2CO3 Lewis structure, molecular geometry, hybridization, polar or nonpolar – Pinterest
• [Chemistry] Lewis Structure for H2CO3 – Does it matter how it looks? – Reddit
• H2CO3 Lewis Structure, Molecular Geometry, Hybridization, and MO Diagram – Techiescientist
• Draw the best lewis structure for h 2 ​ co 3 ​ and calculate the formal charge on carbon – Brainly
• Draw the Lewis structure of carbonic acid, H₂CO₃? – Quizlet
• Carbonic Acid (H2CO3)| Structure & Properties – What’s Insight
• What is correct Lewis structure for carbonic acid H2CO3? – Course Hero
• Draw the Lewis structure and geometry shape for H2CO3 – Bartleby
• Illustrated Glossary of Organic Chemistry – Carbonic acid – UCLA Chemistry
• 61) Which is a correct Lewis structure for carbonic acid, H₂CO₃? – Numerade