CH₂O Lewis Structure

Formaldehyde (methanal) · A preservative and resin precursor, and the simplest aldehyde.

• 12 valence e−
• trigonal planar
• 120° bond angle
• sp²
• polar

Calculated properties

How to draw the CH₂O Lewis structure

1. Count the valence electrons

   Add up the outer-shell electrons every atom brings. That total is the budget for the whole structure - every line and every dot has to come out of it, and nothing may be added.

   4 (C) + 2 x 1 (H) + 6 (O) = 12 valence electrons

2. Choose the central atom

   Carbon is the central atom - it forms four bonds and is never terminal in these molecules.

3. Join everything with single bonds first

   Every connection starts as one shared pair. Draw them all before worrying about double bonds - the arithmetic in the next step is what tells you where the double bonds have to go.

   3 bonds x 2 = 6 electrons used, 6 left

4. Work out how far short you are

   Add up what every atom still needs to fill its shell - eight electrons for most atoms, two for hydrogen - minus what its single bonds already give it. Compare that with the electrons you have left. The difference decides everything that follows.

   needs 8, has 6, short by 2

5. Turn the shortfall into multiple bonds

   Being short means atoms have to share more. Every pair that moves from a lone pair into a bond counts twice - once for each atom - so a shortfall of 2 is covered by 1 extra shared pair. That is where the double bond comes from.

   C=O

6. Fill in the lone pairs

   Every electron not in a bond sits as a lone pair on an atom. Each atom takes exactly what it needs to finish its shell - there is no choice left at this point.

   O: 2 (4 electrons)

7. Check the central atom

   C ends up with a full octet. Every electron in the budget is now placed.

   C: 8 bonding + 0 nonbonding = 8

8. Check the formal charges

   Formal charge is valence electrons, minus lone-pair electrons, minus the number of bonds. Every atom here comes out at zero, which is the sign of a good structure.

   all formal charges = 0

9. Work out the shape

   Count the electron domains on C: 3 bonded groups. A double or triple bond still counts as one domain, because it points in one direction. That gives trigonal planar electron geometry; ignore the lone pairs and the atoms themselves sit in a trigonal planar arrangement.

   steric number 3 -> sp2 -> trigonal planar, bond angle 120

10. Decide whether it is polar

    The atoms around the centre are not all the same, so the bond dipoles are different sizes and cannot cancel.

    dipoles do not cancel -> polar

Is CH₂O polar or nonpolar?

CH₂O is polar. The atoms around the centre are not all the same, so the bond dipoles are different sizes and cannot cancel.

Common questions

How many valence electrons does CH₂O have?

CH₂O has 12 valence electrons. 8 of them are in bonds and 4 sit in lone pairs.

What is the molecular geometry of CH₂O?

CH₂O is a trigonal planar molecule. The central C has 3 bonded groups, a steric number of 3, which gives trigonal planar electron geometry and a trigonal planar molecule.

What is the bond angle in CH₂O?

The bond angle in CH₂O is 120 degrees. That is the ideal trigonal planar angle, and nothing distorts it here.

What is the hybridization of CH₂O?

The central C in CH₂O is sp² hybridized. Steric number 3 means 3 orbitals have to be mixed, which is exactly what sp² gives you.

Is CH₂O polar or nonpolar?

CH₂O is polar. The atoms around the centre are not all the same, so the bond dipoles are different sizes and cannot cancel.

Related molecules

• C₂H₄ also built around C
• C₆H₆ also built around C
• SO₃ also trigonal planar
• BF₃ also trigonal planar
• HNO₃ also trigonal planar
• CO₂ also built around C