Now recall there are many possible Lewis dot structures that exist, but there are rules to draw the best structure. Here we have to determine the electron geometry for the following molecule of CH2O. Alright. So here the number of valence electrons; we have carbon, which is in group 4A, hydrogen, which is in group 1A, and there's 2 of them, and we have oxygen, which is in group 6A. So that's 12 total valence electrons.
We put carbon in the center because, remember, hydrogen never goes in the center. We form single bonds to the hydrogen and to the oxygen initially. We place enough electrons around the central elements so they follow the octet rule. But remember, hydrogen doesn't follow the octet rule; it follows the duet rule, so it only needs a single bond and it's fine. At this moment, we've used all 12 of our electrons, so there's none left. Remember, bonding preferences: oxygen wants to make 2 bonds and carbon ideally wants to have 4. To accommodate both of them, we'd remove 1 of the lone pairs on oxygen and use it to make a double bond. So this would be the structure of our compound of CH2O, also known as formaldehyde.
So, we'd say it has how many groups attached to it, the central element? 1, 2, 3 electron groups. Remember, when you have 3 electron groups, 3 is tri, so this is trigonal planar or planar. Thus, this will be the electron geometry of the following compound.