Recall there are many possible Lewis dot structures that exist, but there are rules to draw the best structure. So for this example it says determine the electron geometry for the following molecule CH2O. This is also called formaldehyde. So if we take a look here we place the least electronegative element in the center. Now that would be hydrogen. But remember we have another rule when it comes to hydrogen. It can never go in the center. So as a result, it's carbon that has to go in the center.
Carbon is in Group 4A, so it has four valence electrons. And remember, hydrogens are in Group 1A and they can only form single bonds. Carbon itself has to make four bonds. It's already making two bonds. It needs two more. The only element that's left is oxygen, so carbon would have to form a double bond to that oxygen. Carbon oxygens in Group 6A, so it has six valence electrons, and here we're showing all of them. So this would represent the structure or molecular shape of formaldehyde.
Now if we take a look, we'd say that the carbon is connected to how many electron groups it's connected to. 123 electron groups? Remember 3. We say try equals 3 because we're saying try. That would mean that the electronic geometry is trigonal planar, so this would be the electronic geometry or molecular shape of the formaldehyde molecule.