Lewis Structure for CH₂O: Formaldehyde

Lewis structure for CH₂O

$$\begin{array}{ccccc} &&\mathrm{H}&&\\ &&|&&\\ \mathrm{H}&-&\mathrm{C}&=&\underset{\cdot\cdot}{\overset{\cdot\cdot}{\mathrm{O}}} \end{array}$$

Formaldehyde has two C–H single bonds, one C=O double bond, and two lone pairs on oxygen. No lone pairs belong on carbon or hydrogen. The dots above and below oxygen are its four nonbonding electrons.

Start with the correct skeleton

The named molecule is formaldehyde, so both hydrogens and oxygen attach to carbon. Hydrogen can make only one ordinary covalent bond and must remain terminal. Carbon can connect to all three other atoms, making it the central atom in this structure.

The available valence electrons are:

$$4+2(1)+6=12.$$

The three initial single bonds use six electrons. Placing the remaining six on oxygen fills oxygen's octet but leaves carbon with only six surrounding electrons. Convert one oxygen lone pair into a second C–O bonding pair. This forms the double bond without changing the twelve-electron total.

Audit the completed structure

The formal charges are C: 4 − 0 − 4 = 0; O: 6 − 4 − 2 = 0; and each H: 1 − 0 − 1 = 0. The drawing therefore represents neutral CH₂O with complete second-row octets. Its right-angle layout is a convenient Lewis diagram, not a claim that the molecule has 90° bond angles.