CH2O Lewis structure

CH₂O (formaldehyde) has one carbon atom, two hydrogen atoms, and one oxygen atom.

In the CH₂O Lewis structure, there are two single bonds around the carbon atom, with two hydrogen atoms attached to it. And the oxygen atom with two lone pairs on it, makes a double bond with the carbon atom.

Alternative method: Lewis structure of CH₂O

Contents

Rough sketch

First, determine the total number of valence electrons

In the periodic table, carbon lies in group 14, hydrogen lies in group 1, and oxygen lies in group 16.

Hence, carbon has four valence electrons, hydrogen has one valence electron, and oxygen has six valence electrons.

Since CH₂O has one carbon atom, two hydrogen atoms, and one oxygen atom, so…

Valence electrons of one carbon atom = 4 × 1 = 4
Valence electrons of two hydrogen atoms = 1 × 2 = 2
Valence electrons of one oxygen atom = 6 × 1 = 6

And the total valence electrons = 4 + 2 + 6 = 12

Learn how to find: Carbon valence electrons, Hydrogen valence electrons, and Oxygen valence electrons

Second, find the total electron pairs

We have a total of 12 valence electrons. And when we divide this value by two, we get the value of total electron pairs.

Total electron pairs = total valence electrons ÷ 2

So the total electron pairs = 12 ÷ 2 = 6

Third, determine the central atom

Here hydrogen can not be 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.

Now we have to choose the central atom from carbon and oxygen. Place the least electronegative atom at the center.

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

Therefore, place carbon in the center and hydrogen and oxygen on either side.

And finally, draw the rough sketch

CH2O Lewis Structure (Step 1) — Rough sketch of CH₂O Lewis structure | Image: Learnool

Lone pair

Here, we have a total of 6 electron pairs. And three bonds are already marked. So we have to only mark the remaining three electron pairs as lone pairs on the sketch.

Also remember 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.

Always start to mark the lone pairs from outside atoms. Here, the outside atoms are hydrogens and oxygen. But no need to mark on hydrogen, because each hydrogen has already two electrons.

So for oxygen, there are three lone pairs, and for carbon, there is zero lone pair because all three electron pairs are over.

Mark the lone pairs on the sketch as follows:

CH2O Lewis Structure (Step 2) — Lone pairs marked on CH₂O Lewis structure | Image: Learnool

Formal charge

Use the following formula to calculate the formal charges on atoms:

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

For carbon atom, formal charge = 4 – 0 – ½ (6) = +1

For each hydrogen atom, formal charge = 1 – 0 – ½ (2) = 0

For oxygen atom, formal charge = 6 – 6 – ½ (2) = -1

← Scroll horizontally to view all columns →

Atom	Valence electrons	Non-bonding electrons	Bonding electrons	Formal charge
Carbon	4	0	6	+1
Hydrogen (all)	1	0	2	0
Oxygen	6	6	2	-1

Here, both carbon and oxygen atoms have charges, so mark them on the sketch as follows:

CH2O Lewis Structure (Step 3) — Formal charges marked on CH₂O Lewis structure | Image: Learnool

The above structure is not a stable Lewis structure because both carbon and oxygen atoms have charges. Therefore, reduce the charges (as below) by converting lone pairs to bonds.

Convert a lone pair of the oxygen atom to make a new C — O bond with the carbon atom as follows:

CH2O Lewis Structure (Step 4) — Lone pair of oxygen is converted, and got the stable Lewis structure of CH₂O | Image: Learnool

Final structure

The final structure of CH₂O features a central carbon atom connected to an oxygen atom via a double covalent bond and to two hydrogen atoms through single bonds. In this configuration, the carbon atom satisfies the octet rule by forming four total bonds. The oxygen atom fulfills its octet by retaining two lone pairs of its own, while each hydrogen atom reaches its stable duet state through its single shared bond. This setup is the most stable because it results in formal charges of zero for every atom, representing the most energetically favorable state for the molecule. As a result, this specific electronic distribution serves as the definitive and most accurate Lewis representation of formaldehyde.

Next: SO₃ Lewis structure

External video

How to Draw the Lewis Dot Structure for CH2O (Formaldehyde) – YouTube • Wayne Breslyn

External links

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.