The molecule H2C=O, commonly known as formaldehyde, possesses a trigonal planar shape around the carbon atom. In this molecule, the carbon atom forms a double bond with the oxygen atom and single bonds with two hydrogen atoms.
To further explain, the trigonal planar geometry arises because of the carbon’s sp2 hybridization. This type of hybridization involves one s orbital and two p orbitals combining to create three equivalent sp2 hybrid orbitals. These three orbitals are arranged in a plane at 120-degree angles from one another. With the double bond to oxygen and the single bonds to the two hydrogen atoms, this geometric arrangement minimizes electron pair repulsion, according to VSEPR theory, leading to the observed trigonal planar shape.
The oxygen atom has two lone pairs, but since we focus on the shape around the central carbon atom, they do not affect the overall arrangement of the hydrogen atoms and the double bond. This molecular geometry is important as it leads to the unique reactive and physical properties of formaldehyde.